Emotional lateralization
Encyclopedia
Emotional lateralization is the asymmetrical representation of emotional control and processing in the brain. There is evidence for the lateralization of other brain functions
too.
Emotion
s are complex and involve a variety of physical and cognitive responses, many of which are not well understood. The general purpose of emotions is to produce a specific response to a stimulus. Feelings are the conscious perception of emotions, and when an emotion occurs frequently or continuously this is called a mood.
A variety of scientific studies have found lateralization of emotions. FMRI and lesion
studies have shown asymmetrical activation of brain regions while thinking of emotions, responding to extreme emotional stimuli, and viewing emotional situations. Processing and production of facial expressions also appear to be asymmetric in nature. Many theories of lateralization have been proposed and some of those specific to emotions. Please keep in mind most the information in this article is theoretical and scientists are still trying to understand emotion and emotional lateralization. Also, some of the evidence is contradictory. Many brain regions are interconnected and the input and output of any given region may come from and go to many different regions.
a) The right hemisphere has more control over emotion than left hemisphere.Lane, p. 79-80.
b) The right hemisphere is dominant in emotional expression in a similar way that the left hemisphere is dominant in language.
c) The right hemisphere is dominant in the perception of facial expression, body posture, and prosody
.
d) The right hemisphere is important for processing primary emotions such as fear while the left hemisphere is important for preprocessing social emotions. Lane, p. 332.
General lesions in the right hemisphere reduce or eliminate electrodermal response (skin conductance response)(SCR) to emotionally meaningful stimuli while the lesions in the left hemisphere do not show changes in SCR response.Lane, p. 192.
Subject SB-2046 had part of his right, prefrontal lobe removed because of cancer. While his IQ and a majority of other normal functions were unharmed, he had severely impaired decision-making skills especially when he had to consider immediate vs. future reward and punishment. His decisions were almost always guided by immediate reward or punishment and disregarded any long-term consequences. Researchers were incapable of conditioning
patient SB-2046 to nonverbal stimuli containing emotional meaning (reward or punishment), but were able to condition the patient to verbal stimuli containing emotional meaning.
Most language production
and processing occur in the left hemisphere while the majority of the emotional processing and production of emotion in speech occurs in the right hemisphere. Schizophrenic patients usually have difficulty processing prosody. These patients also show a remarkable increase in lateralization towards the right hemisphere of both emotionally and non-emotional prosody rich speech. Also, a decrease in right-handedness led to an increase in the right hemisphere lateralization. This right hemisphere lateralization extends beyond prosody to many of aspects of language and speech processing in schizophrenic patients.
a) Left hemisphere primarily process "negative" emotions and right hemisphere primarily process "positive" emotions. A large portion of regions primarily in the right hemisphere are activated during aversive classical conditioning
.Lane, p. 233-237.
b) Other divisions of specialization
is not symmetrical. Afferent nerves in the parasympathetic and sympathetic systems of the autonomic nervous system differently innervate various organs that maintain homeostasis
such as the heart and the face. The asymmetrical representation of the autonomic peripheral nervous system leads to the asymmetrical representation in the brain. The left hemisphere is activated predominantly by homeostatic afferents associated with parasympathetic functions and the right hemisphere is activated predominantly by homeostatic afferents associated with sympathetic functions. The lateralization is extremely apparent in the anterior cingulate cortex
(ACC) and anterior insular cortex
(AI) associated with higher emotions such as romantic love and motivation correlated with homeostatic functions. The left AI and ACC are more active during feelings of romantic love and maternal attachment. The AI and ACC were activated on both the right and left sides while watching pain being inflicted on a loved one while only the right AI and ACC that is elicited during subjective feelings of pain; this supports the association of right AI in aroused (‘sympathetic’) feelings and left AI in affiliative (‘parasympathetic’) feelings.
Particularly, cardiovascular function appears to be lateralized and tied to emotional stress. Intense emotional stimuli that cause stress can lead to alterations in cardiovascular function. The right insular cortex probably plays the most significant role in these phenomena. Similar lateralization is probably involved in cardiovascular malfunction in patients with head injury, stroke, multiple sclerosis, brain tumors, meningitis and encephalitis, migraine, cluster headache and neurosurgical procedures.
waves in the parietal
and frontal lobes. Negative pictures activated the left hemisphere in women more than in men, and the right hemisphere in men more than in women when shown unpleasant images.
, skin conductance response (SCR), standardized tests ranging from cognitive (e.g. IQ tests) to emotional intelligence, and subjective questionnaires such as those rating how fearful or happy faces look. All the tests have their strengths and weakness (see "Limitation of Studies" below). This section primarily focuses on results on the more subjective observations and results that have unknown neural basis or regions.
Situations that contradict moral teachings generally produce negative emotions. Watching people behave badly by breaking moral codes most significantly activates the right parahippocampal gyrus
, the right medial frontal gyrus
, and left amygdala
. Watching emotionally negative situations most significantly activates the right amygdala. This study indicates that lateral processing of emotions extends beyond the basic emotions to higher cognitive responses.
Depression or having previously been depressed probably is due to altered brain structure or alters brain structure. Patients who have been depressed or are depressed show more activation to negative stimuli in emotion. When negative stimuli were presented to patients' right hemispheres, the patients were significantly more accurate and quicker to respond to the stimuli. The data in this study shows that psychological disorders are correlated with increased lateralization.
Chimpanzees, other primates, and humans produce asymmetrical facial expressions with greater expression on the left side of the face (right hemisphere of the brain). Researchers also subjectively reported that the left side of the face was expressed more emotion using images of left-left chimeric faces.
was reciprocally associated with decrease activity in the amygdala. These findings imply that the prefrontal cortex modulates the amygdala activity. The left prefronatal cortex plays a role in approach behaviors (positively valanced emotions), while the amygdala plays a role in withdrawal behaviors (negatively valenced emotions).Lane, p. 383
is the most significantly activated region while processing sadness.
Patients with inferior frontal lobe
damage produce less and less intense facial expression when presented with emotional stimuli, and they also have problems reading fear and disgust in other people. People with left inferior frontal lobe damage produced less facial expression and could not analyze emotional situations as well as those with right frontal lobe damage especially with fear and disgust. The left inferior frontal gyrus
(IFG) plays an important role in anger while the right IFG plays a larger role in disgust.
Patients with dorsolateral frontal cortex lesions have difficulty discerning propositional attitude
. Patients with left lesions show further increased impairment.
) and posterior (angular gyrus
) regions resulted in reduced SCR. Damage to the right hemisphere in these regions resulted in a significant (p < 0.001) decrease in SCR while the damage to the left hemisphere of these regions did not (p > 0.05).Lane, p. 192-195.
was the most significantly activated area during the processing happiness. The right superior temporal gyrus increasingly responds to an increasingly happy stimuli, while the left pulvinar
increasingly responds to increasingly fearful stimuli. The right pulvinar is activated during aversive conditioning.
plays a key role in emotional processing especially fear, and amygdala function appears to be emotionally lateralized. When people are shown fearful faces the left amygdala and left periamygdalooid cortex
increase in activation. There also appears to be a greater increase in neural activity in the left amygdala corresponding to an increasingly fearful stimulus.Lane, p. 228-230 Recordings from single-unit electrodes in monkeys have shown similar activation in the left amygdala. A man with confined damage in the right amygdala could not produce a startle response.Lane, p. 117-120. The activity (measured by a PET scan) in the right amygdala correlated to the number of emotionally arousing film clips capable of being recalled in patients.
Unilateral activation of the amygdala due to fearful stimuli may also produce unilateral activation of other regions. The right middle temporal gyrus, right brainstem, left hippocampus
, right cerebellum
, right fuisform gyrus
, and left lingual gyrus
were also activated during fearful stimuli. Activation of multiple brain regions both indicates that emotions are processed in many parts of the brain and that emotions are complex.
The amygdala probably plays in the conscious processing of emotion. The left amygdala was activated during the processing of conscious stimuli while the right amygdala was active during the processing of nonconscous stimuli.
(ACC) plays a role in a variety of functions including emotional ones. The ACC may be important in conscious awareness of emotion.Lane, p. 359-361. Damage to the ACC is associated with decreased SCR to physical and psychological stimuli. Bilateral and unilateral damage both resulted in decreased SCR indicates that the right and left ACC's may specialized in certain aspects of emotional response.
(AI) increasingly responds to increasingly fearful stimuli. The AI may also be involved in the conscious experience of emotion.
Symptoms that arise from confined regions of damage usually have stereotypical emotional and behavioral changes. Diagnosis for locating damaged regions that process emotion may aided by noticeable emotional changes categorized under one of the lateralized emotional control systems. Diagnosis and treatment for cardiovascular irregularities that arises from emotions states could be aided by understanding the physical basis of the psychological influences. Instead of treating the cardiovascular irregularities for psychological issues, treatment could target the lateralized brain regions.
ing. Since very few extremes cases exist the sample size of human studies of emotional lateralization are generally very limited and may be as small as single person. While these studies may provide a good insight into certain brain region functions, the studies may not provide information for the general information. Animal studies may fix this problem but emotions in humans are generally more complicated than in animals.
or PET
to study emotional responses. Because fMRI measures changes in blood oxygenation, using the BOLD effect, its temporal resolution is limited by the haemodynamic response
to several seconds. PET has similar limits, offering slightly better temporal resolution and slightly worse spatial resolution.
Lateralization of brain function
A longitudinal fissure separates the human brain into two distinct cerebral hemispheres, connected by the corpus callosum. The sides resemble each other and each hemisphere's structure is generally mirrored by the other side. Yet despite the strong anatomical similarities, the functions of each...
too.
Emotion
Emotion
Emotion is a complex psychophysiological experience of an individual's state of mind as interacting with biochemical and environmental influences. In humans, emotion fundamentally involves "physiological arousal, expressive behaviors, and conscious experience." Emotion is associated with mood,...
s are complex and involve a variety of physical and cognitive responses, many of which are not well understood. The general purpose of emotions is to produce a specific response to a stimulus. Feelings are the conscious perception of emotions, and when an emotion occurs frequently or continuously this is called a mood.
A variety of scientific studies have found lateralization of emotions. FMRI and lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
studies have shown asymmetrical activation of brain regions while thinking of emotions, responding to extreme emotional stimuli, and viewing emotional situations. Processing and production of facial expressions also appear to be asymmetric in nature. Many theories of lateralization have been proposed and some of those specific to emotions. Please keep in mind most the information in this article is theoretical and scientists are still trying to understand emotion and emotional lateralization. Also, some of the evidence is contradictory. Many brain regions are interconnected and the input and output of any given region may come from and go to many different regions.
Right Hemisphere Dominance
Some variations of right hemisphere dominance are...a) The right hemisphere has more control over emotion than left hemisphere.Lane, p. 79-80.
b) The right hemisphere is dominant in emotional expression in a similar way that the left hemisphere is dominant in language.
c) The right hemisphere is dominant in the perception of facial expression, body posture, and prosody
Prosody (linguistics)
In linguistics, prosody is the rhythm, stress, and intonation of speech. Prosody may reflect various features of the speaker or the utterance: the emotional state of the speaker; the form of the utterance ; the presence of irony or sarcasm; emphasis, contrast, and focus; or other elements of...
.
d) The right hemisphere is important for processing primary emotions such as fear while the left hemisphere is important for preprocessing social emotions. Lane, p. 332.
General lesions in the right hemisphere reduce or eliminate electrodermal response (skin conductance response)(SCR) to emotionally meaningful stimuli while the lesions in the left hemisphere do not show changes in SCR response.Lane, p. 192.
Subject SB-2046 had part of his right, prefrontal lobe removed because of cancer. While his IQ and a majority of other normal functions were unharmed, he had severely impaired decision-making skills especially when he had to consider immediate vs. future reward and punishment. His decisions were almost always guided by immediate reward or punishment and disregarded any long-term consequences. Researchers were incapable of conditioning
Classical conditioning
Classical conditioning is a form of conditioning that was first demonstrated by Ivan Pavlov...
patient SB-2046 to nonverbal stimuli containing emotional meaning (reward or punishment), but were able to condition the patient to verbal stimuli containing emotional meaning.
Most language production
Language production
In psycholinguistics, language production is the production of spoken or written language. It describes all of the stages between having a concept, and translating that concept into linguistic form...
and processing occur in the left hemisphere while the majority of the emotional processing and production of emotion in speech occurs in the right hemisphere. Schizophrenic patients usually have difficulty processing prosody. These patients also show a remarkable increase in lateralization towards the right hemisphere of both emotionally and non-emotional prosody rich speech. Also, a decrease in right-handedness led to an increase in the right hemisphere lateralization. This right hemisphere lateralization extends beyond prosody to many of aspects of language and speech processing in schizophrenic patients.
Complementarity specialization
The two hemispheres have a complementary specialization for control of different aspects of emotion.a) Left hemisphere primarily process "negative" emotions and right hemisphere primarily process "positive" emotions. A large portion of regions primarily in the right hemisphere are activated during aversive classical conditioning
Classical conditioning
Classical conditioning is a form of conditioning that was first demonstrated by Ivan Pavlov...
.Lane, p. 233-237.
-
- While this theory seems to hold true for some emotions, this theory is generally considered outdated; however a few examples exist. For example, a study found that when subjects were primed with positive stimuli before hearing a consonant, the left hemisphere was more active than the right hemisphere. In contrast, when subjects were primed with a negative stimulus, the right hemisphere was more active than the left hemisphere.
b) Other divisions of specialization
-
- The amygdalaAmygdalaThe ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
plays a role in the conscious awareness of emotion (feelings) resulting in perception of feeling, but experiments suggest the left and right amygdala have distinct roles in conscious and unconscious processing of emotion. The right amygdala plays a role in the nonconscious processing of emotion while the left amygdala was involved in the processing of conscious emotions.Lane, p. 321. These results were obtained from studies that maskedBackmaskingBackmasking is a recording technique in which a sound or message is recorded backward on to a track that is meant to be played forward...
conditioning stimuli. Stimuli were presented over a very short period of time such that subjects were not consciously aware of the stimuli but were still able to show physiological changes.
- The amygdala
-
- Damage to the left hemisphere in patients results in a marked increase in depression.Lane, p. 334-339. ValenceValence (psychology)Valence, as used in psychology, especially in discussing emotions, means the intrinsic attractiveness or aversiveness of an event, object, or situation. However, the term is also used to characterize and categorize specific emotions. For example, the emotions popularly referred to as "negative",...
asymmetry may be due to more cholinergicCholinergicThe word choline generally refers to the various quaternary ammonium salts containing the N,N,N-trimethylethanolammonium cation. Found in most animal tissues, choline is a primary component of the neurotransmitter acetylcholine and functions with inositol as a basic constituent of lecithin...
and dopaminergicDopaminergicDopaminergic means related to the neurotransmitter dopamine. For example, certain proteins such as the dopamine transporter , vesicular monoamine transporter 2 , and dopamine receptors can be classified as dopaminergic, and neurons which synthesize or contain dopamine and synapses with dopamine...
on the left hemisphere and the right hemisphere being more noradrenergic. Patients with right hemisphere damage had reduced arousal response to painful stimuli.
- Damage to the left hemisphere in patients results in a marked increase in depression.Lane, p. 334-339. Valence
Homeostatic Basis
This model provides a neuroanatomical basis for emotional control and processing. The peripheral autonomic nervous systemAutonomic nervous system
The autonomic nervous system is the part of the peripheral nervous system that acts as a control system functioning largely below the level of consciousness, and controls visceral functions. The ANS affects heart rate, digestion, respiration rate, salivation, perspiration, diameter of the pupils,...
is not symmetrical. Afferent nerves in the parasympathetic and sympathetic systems of the autonomic nervous system differently innervate various organs that maintain homeostasis
Homeostasis
Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...
such as the heart and the face. The asymmetrical representation of the autonomic peripheral nervous system leads to the asymmetrical representation in the brain. The left hemisphere is activated predominantly by homeostatic afferents associated with parasympathetic functions and the right hemisphere is activated predominantly by homeostatic afferents associated with sympathetic functions. The lateralization is extremely apparent in the anterior cingulate cortex
Anterior cingulate cortex
The anterior cingulate cortex is the frontal part of the cingulate cortex, that resembles a "collar" form around the corpus callosum, the fibrous bundle that relays neural signals between the right and left cerebral hemispheres of the brain...
(ACC) and anterior insular cortex
Insular cortex
In each hemisphere of the mammalian brain the insular cortex is a portion of the cerebral cortex folded deep within the lateral sulcus between the temporal lobe and the frontal lobe. The cortical area overlying it towards the lateral surface of the brain is the operculum...
(AI) associated with higher emotions such as romantic love and motivation correlated with homeostatic functions. The left AI and ACC are more active during feelings of romantic love and maternal attachment. The AI and ACC were activated on both the right and left sides while watching pain being inflicted on a loved one while only the right AI and ACC that is elicited during subjective feelings of pain; this supports the association of right AI in aroused (‘sympathetic’) feelings and left AI in affiliative (‘parasympathetic’) feelings.
Particularly, cardiovascular function appears to be lateralized and tied to emotional stress. Intense emotional stimuli that cause stress can lead to alterations in cardiovascular function. The right insular cortex probably plays the most significant role in these phenomena. Similar lateralization is probably involved in cardiovascular malfunction in patients with head injury, stroke, multiple sclerosis, brain tumors, meningitis and encephalitis, migraine, cluster headache and neurosurgical procedures.
Lateralization due to lateralization of other functions
"It is unlikely that the brain evolved an asymmetrical control of emotional behavior. Rather, it seems more likely that although there may be some asymmetry in the neural control of emotion, the observed asymmetries are largely a product of the asymmetrical control of other functions such as the control of movement, language, or the processing of complex sensory information," Lateralization may have been evolutionarily adaptive. Lateralization may allow for a greater variety of emotions. The left temporal cortex is involved in language processing while the right temporal cortex is involved in processing faces. This lateralization is also apparent when processing emotions.Lateralization and Sex Differences
There may be a difference in cortical activation between men and women. Activity in the right hemisphere was greater in women when exposed to unpleasant images than men, though men showed more activation bilaterally while viewing pleasant pictures.Lane, p. 261. Another study found that women but not men, with women had greater activation of their right hemisphere while viewing unpleasant faces and left hemisphere activation while viewing pleasant faces. Yet, another study found contrasting sex difference while recording EEGEEG
EEG commonly refers to electroencephalography, a measurement of the electrical activity of the brain.EEG may also refer to:* Emperor Entertainment Group, a Hong Kong-based entertainment company...
waves in the parietal
Parietal lobe
The parietal lobe is a part of the Brain positioned above the occipital lobe and behind the frontal lobe.The parietal lobe integrates sensory information from different modalities, particularly determining spatial sense and navigation. For example, it comprises somatosensory cortex and the...
and frontal lobes. Negative pictures activated the left hemisphere in women more than in men, and the right hemisphere in men more than in women when shown unpleasant images.
Evidence of Lateralization
The vast majority of the data comes from functional imagingFunctional imaging
Functional imaging , is a method of detecting or measuring changes in metabolism, blood flow, regional chemical composition, and absorption....
, skin conductance response (SCR), standardized tests ranging from cognitive (e.g. IQ tests) to emotional intelligence, and subjective questionnaires such as those rating how fearful or happy faces look. All the tests have their strengths and weakness (see "Limitation of Studies" below). This section primarily focuses on results on the more subjective observations and results that have unknown neural basis or regions.
Behavioral Differences & Cortical Activation
70% of right handed patients show preference in expressing emotion on the right side of their face; this was determined using chimeric faces produced using right-right or left-left mirrored faces. The left side of the face seems more fluent in expressing emotions which means the right cortical hemisphere is more fluent in expressing emotions.Lane, p. 71-73. Handedness does not appear to affect the processing associated with viewing facial expressions.Situations that contradict moral teachings generally produce negative emotions. Watching people behave badly by breaking moral codes most significantly activates the right parahippocampal gyrus
Parahippocampal gyrus
The parahippocampal gyrus is a grey matter cortical region of the brain that surrounds the hippocampus. This region plays an important role in memory encoding and retrieval....
, the right medial frontal gyrus
Medial frontal gyrus
The superior frontal gyrus is situated above the superior frontal sulcus and is continued on to the medial surface of the hemisphere, the medial frontal gyrus...
, and left amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
. Watching emotionally negative situations most significantly activates the right amygdala. This study indicates that lateral processing of emotions extends beyond the basic emotions to higher cognitive responses.
Depression or having previously been depressed probably is due to altered brain structure or alters brain structure. Patients who have been depressed or are depressed show more activation to negative stimuli in emotion. When negative stimuli were presented to patients' right hemispheres, the patients were significantly more accurate and quicker to respond to the stimuli. The data in this study shows that psychological disorders are correlated with increased lateralization.
Facial Expressions of Emotion
Patients with damage to their left amygdala lesions rated fearful faces less fearful than normal subjects. Similar findings showed that regional blood flow increased in response to fear faces while decreased to euphoric faces in the left amygdala.Chimpanzees, other primates, and humans produce asymmetrical facial expressions with greater expression on the left side of the face (right hemisphere of the brain). Researchers also subjectively reported that the left side of the face was expressed more emotion using images of left-left chimeric faces.
Notable Lateralized Brain Structures & Regions
Emotion is processed in many different areas of the brain, and a specific emotion may be processed in multiple areas. Regions involved in emotional lateralization appear to follow the general conventions that describe the roles/functions of certain brain regions. Below are a few regions and structure involved in emotional processing that show functional lateralization.Prefrontal Lobe
Using a PET scan, researchers found that activity in the left medial and lateral prefrontal cortexPrefrontal cortex
The prefrontal cortex is the anterior part of the frontal lobes of the brain, lying in front of the motor and premotor areas.This brain region has been implicated in planning complex cognitive behaviors, personality expression, decision making and moderating correct social behavior...
was reciprocally associated with decrease activity in the amygdala. These findings imply that the prefrontal cortex modulates the amygdala activity. The left prefronatal cortex plays a role in approach behaviors (positively valanced emotions), while the amygdala plays a role in withdrawal behaviors (negatively valenced emotions).Lane, p. 383
Frontal Lobe
The superior frontal gyrusSuperior frontal gyrus
The superior frontal gyrus makes up about one-third of the frontal lobe of the human brain. It is bounded laterally by the superior frontal sulcus....
is the most significantly activated region while processing sadness.
Patients with inferior frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
damage produce less and less intense facial expression when presented with emotional stimuli, and they also have problems reading fear and disgust in other people. People with left inferior frontal lobe damage produced less facial expression and could not analyze emotional situations as well as those with right frontal lobe damage especially with fear and disgust. The left inferior frontal gyrus
Inferior frontal gyrus
The inferior frontal gyrus is a gyrus of the frontal lobe . It is labelled gyrus frontalis inferior, its Latin name...
(IFG) plays an important role in anger while the right IFG plays a larger role in disgust.
Patients with dorsolateral frontal cortex lesions have difficulty discerning propositional attitude
Propositional attitude
A propositional attitude is a relational mental state connecting a person to a proposition. They are often assumed to be the simplest components of thought and can express meanings or content that can be true or false...
. Patients with left lesions show further increased impairment.
Parietal Lobe
Damage to the inferior parietal region including the anterior (supramarginal gyrusSupramarginal gyrus
The supramarginal gyrus is a portion of the parietal lobe. It is probably involved with language perception and processing, and lesions in it may cause Wernicke's aphasia or transcortical sensory aphasia.-External links:...
) and posterior (angular gyrus
Angular gyrus
The angular gyrus is a region of the brain in the parietal lobe, that lies near the superior edge of the temporal lobe, and immediately posterior to the supramarginal gyrus; it is involved in a number of processes related to language, mathematics and cognition...
) regions resulted in reduced SCR. Damage to the right hemisphere in these regions resulted in a significant (p < 0.001) decrease in SCR while the damage to the left hemisphere of these regions did not (p > 0.05).Lane, p. 192-195.
Temporal Lobe
The right superior temporal gyrusSuperior temporal gyrus
The superior temporal gyrus is one of three gyri in the temporal lobe of the human brain, which is located laterally to the head, situated somewhat above the external ear.The superior temporal gyrus is bounded by:* the lateral sulcus above;...
was the most significantly activated area during the processing happiness. The right superior temporal gyrus increasingly responds to an increasingly happy stimuli, while the left pulvinar
Pulvinar
The pulvinar nuclei are a collection of nuclei located in the pulvinar thalamus. The pulvinar part is the most posterior region of the thalamus....
increasingly responds to increasingly fearful stimuli. The right pulvinar is activated during aversive conditioning.
Amygdala
The amygdalaAmygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
plays a key role in emotional processing especially fear, and amygdala function appears to be emotionally lateralized. When people are shown fearful faces the left amygdala and left periamygdalooid cortex
Periamygdaloid cortex
Periamygdaloid cortex is a portion of the rhinencephalon consisting of paleocortex.The periamygdaloid cortex plays a role in olfaction.It has been suggested that the left periamygdalar region may play a role in yawning....
increase in activation. There also appears to be a greater increase in neural activity in the left amygdala corresponding to an increasingly fearful stimulus.Lane, p. 228-230 Recordings from single-unit electrodes in monkeys have shown similar activation in the left amygdala. A man with confined damage in the right amygdala could not produce a startle response.Lane, p. 117-120. The activity (measured by a PET scan) in the right amygdala correlated to the number of emotionally arousing film clips capable of being recalled in patients.
Unilateral activation of the amygdala due to fearful stimuli may also produce unilateral activation of other regions. The right middle temporal gyrus, right brainstem, left hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
, right cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
, right fuisform gyrus
Fusiform gyrus
The fusiform gyrus is part of the temporal lobe in Brodmann Area 37. It is also known as the occipitotemporal gyrus. Other sources have the fusiform gyrus above the occipitotemporal gyrus and underneath the parahippocampal gyrus....
, and left lingual gyrus
Lingual gyrus
The lingual gyrus of the occipital lobe lies between the calcarine sulcus and the posterior part of the collateral sulcus; behind, it reaches the occipital pole; in front, it is continued on to the tentorial surface of the temporal lobe, and joins the parahippocampal gyrus...
were also activated during fearful stimuli. Activation of multiple brain regions both indicates that emotions are processed in many parts of the brain and that emotions are complex.
The amygdala probably plays in the conscious processing of emotion. The left amygdala was activated during the processing of conscious stimuli while the right amygdala was active during the processing of nonconscous stimuli.
Anterior cingulate cortex (ACC)
The anterior cingulate cortexAnterior cingulate cortex
The anterior cingulate cortex is the frontal part of the cingulate cortex, that resembles a "collar" form around the corpus callosum, the fibrous bundle that relays neural signals between the right and left cerebral hemispheres of the brain...
(ACC) plays a role in a variety of functions including emotional ones. The ACC may be important in conscious awareness of emotion.Lane, p. 359-361. Damage to the ACC is associated with decreased SCR to physical and psychological stimuli. Bilateral and unilateral damage both resulted in decreased SCR indicates that the right and left ACC's may specialized in certain aspects of emotional response.
Anterior Insula (AI)
The left anterior insulaInsular cortex
In each hemisphere of the mammalian brain the insular cortex is a portion of the cerebral cortex folded deep within the lateral sulcus between the temporal lobe and the frontal lobe. The cortical area overlying it towards the lateral surface of the brain is the operculum...
(AI) increasingly responds to increasingly fearful stimuli. The AI may also be involved in the conscious experience of emotion.
Implications
Phenomena such as emotional lateralization may help describe how emotions arise, persist, and alter our behavior. Understanding emotional lateralization will help scientist understand emotion in general. Emotional lateralization may also play a role in psychological disorders such as depression and schizophrenia. Future treatment of psychological disorders may have more targeted neurological treatments rather than ingested drugs.Symptoms that arise from confined regions of damage usually have stereotypical emotional and behavioral changes. Diagnosis for locating damaged regions that process emotion may aided by noticeable emotional changes categorized under one of the lateralized emotional control systems. Diagnosis and treatment for cardiovascular irregularities that arises from emotions states could be aided by understanding the physical basis of the psychological influences. Instead of treating the cardiovascular irregularities for psychological issues, treatment could target the lateralized brain regions.
Limitation of Studies
Like all scientific experiments there are limitations of what researchers can do. Attempting to study emotions is especially hard since emotions are complex and can lead to subjective response. An obvious limitation is the majority of the experiments relevant to emotional lateralization have been on fear leaving the question of whether other emotions are also lateralized. Below are two major issues associated with many of the experiments studying emotion that require further explanation.Sample Size
A large percent of the studies provided in humans are of anomalies due to accidents, tumors, or attempting to cure disease (e.g. seizures) using lesionLesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
ing. Since very few extremes cases exist the sample size of human studies of emotional lateralization are generally very limited and may be as small as single person. While these studies may provide a good insight into certain brain region functions, the studies may not provide information for the general information. Animal studies may fix this problem but emotions in humans are generally more complicated than in animals.
Functional Imaging
There are several limitations when using fMRIFunctional magnetic resonance imaging
Functional magnetic resonance imaging or functional MRI is a type of specialized MRI scan used to measure the hemodynamic response related to neural activity in the brain or spinal cord of humans or other animals. It is one of the most recently developed forms of neuroimaging...
or PET
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
to study emotional responses. Because fMRI measures changes in blood oxygenation, using the BOLD effect, its temporal resolution is limited by the haemodynamic response
Haemodynamic response
Haemodynamics is a medical term for the dynamic regulation of the blood flow in the brain. It is the principle on which functional magnetic resonance imaging is based....
to several seconds. PET has similar limits, offering slightly better temporal resolution and slightly worse spatial resolution.