Recurrent thalamo-cortical resonance
Encyclopedia
Recurrent thalamo-cortical resonance
is an observed phenomenon of oscillatory electrical activity between the thalamus
and various cortical regions of the brain. It is proposed by Rodolfo Llinas
and others as a theory for the integration of sensory
perception
into current brain
state. While the role of thalamocortical oscillations in the human
brain is a matter of debate, they are associated with temporal
binding of sensory inputs and thought to be a mechanism of synchronization
between different cortical regions of the brain.
. This oscillation is caused by the activation of leaky P/Q-type calcium channels found in the dendrites of the cells. Because of the leaky channel properties, spontaneous, inherent oscillation can occur independent of any rhythmic input. The ramifications of this capability are not entirely known and may be attributable to background noise into the system. The cortex also links to dendrites of these thalamic cells and serves as the input that drives thalamic oscillation. Physiological oscillation occurs at gamma range of frequencies from 20-50 Hz.
dendrites of pyramidal cells in the cortex. These pyramidal cells reciprocally synapse
back on thalamic neurons. Each loop is self-contained and modulated by sensory input. Inhibitory neurons both in the cortex and the reticular nucleus of the thalamus regulate circuit activity.
afferents specifically at the gamma-band frequency and is an active inhibition: administration of a GABAA blocker stops the effect.
(MEG) has been used to show that during conscious perception, gamma-band frequency electrical activity and thalamocortical resonance occurs in the human brain. Sensory input can be seen to modulate the oscillatory patterns of this activity while awake. 40 Hz oscillation is also seen during REM sleep, but interestingly auditory input does not appear to induce any changes during this sleep state. It appears then that sensory input may be blocked from interfering with the intrinsic state of the brain during REM.
-parietal
cortex. This activity could be generated by pyramidal neurons in layer IV. It has been shown that alpha rhythms seem to be related to the focus of attention: external focus on visual tasks diminish alpha activity while internal focus as in heavy working memory tasks show an increase in alpha magnitudes.
(TCD) is a proposed concept for the disruption of normal gamma-band electrical activity seen between the cortex and thalamic neurons. This state is seen in patients with neuropathic pain
, tinnitus
, and Parkinson’s disease and is characterized by the presence of unusually low-frequency resonance in the thalamocortical system and is associated with disruption of many brain functions including cognition
, sensory perception, and motor control
. TCD occurs when thalamocortical neurons become hyperpolarized, allowing T type calcium channels to activate and the cell’s oscillatory properties to change. A repeated burst of action potentials occurs at lower frequencies in the 4-10 Hz range. These bursts can be sustained by inhibition from the thalamic reticular nucleus and may cause an activation of cortical regions adjacent to the abnormal neurons that are normally inhibited by gamma-band activity. While the effect of the deviation from normal patterns of oscillatory activity in this system is still debatable, it is proposed that the phenomenon can explain chronic pain in cases where there is no peripheral nerve damage.
Resonance
In physics, resonance is the tendency of a system to oscillate at a greater amplitude at some frequencies than at others. These are known as the system's resonant frequencies...
is an observed phenomenon of oscillatory electrical activity between the thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
and various cortical regions of the brain. It is proposed by Rodolfo Llinas
Rodolfo Llinás
Rodolfo R. Llinás PhD is a neuroscientist. He is presently the Thomas and Suzanne Murphy Professor of Neuroscience and Chairman of the department of Physiology & Neuroscience at the NYU School of Medicine...
and others as a theory for the integration of sensory
Sensory
Sensory may refer to:relating to senses or smellIn biology:* Sensory preference* Sensory system, part of the nervous system of organisms* Sensory neuron, nerve cell responsible for transmitting information about external stimuli...
perception
Perception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
into current brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
state. While the role of thalamocortical oscillations in the human
Human
Humans are the only living species in the Homo genus...
brain is a matter of debate, they are associated with temporal
Temporal
Temporal can refer to:* of or relating to time** Temporality in philosophy** Temporal database, a database recording aspects of time varying values** The Temporal power of the Popes of the Roman Catholic Church...
binding of sensory inputs and thought to be a mechanism of synchronization
Synchronization
Synchronization is timekeeping which requires the coordination of events to operate a system in unison. The familiar conductor of an orchestra serves to keep the orchestra in time....
between different cortical regions of the brain.
Thalamic oscillation
Thalamic cells exhibit gamma oscillation when depolarized to greater than -45 mV. The frequency of oscillation is related to the degree of depolarizationDepolarization
In biology, depolarization is a change in a cell's membrane potential, making it more positive, or less negative. In neurons and some other cells, a large enough depolarization may result in an action potential...
. This oscillation is caused by the activation of leaky P/Q-type calcium channels found in the dendrites of the cells. Because of the leaky channel properties, spontaneous, inherent oscillation can occur independent of any rhythmic input. The ramifications of this capability are not entirely known and may be attributable to background noise into the system. The cortex also links to dendrites of these thalamic cells and serves as the input that drives thalamic oscillation. Physiological oscillation occurs at gamma range of frequencies from 20-50 Hz.
Thalamocortical circuits
Thalamic cells synapse on apicalApical
Apical, from the Latin apex meaning to be at the apex or tip, may refer to:*Apical , an anatomical term of location for features associated with the base of an organism or structure...
dendrites of pyramidal cells in the cortex. These pyramidal cells reciprocally synapse
Synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
back on thalamic neurons. Each loop is self-contained and modulated by sensory input. Inhibitory neurons both in the cortex and the reticular nucleus of the thalamus regulate circuit activity.
Inputs to thalamocortical system
The thalamus contains gates information into the thalamocortical loops based on the source of the signal. This is done based on the location that such information enters in the thalamus. Specific inputs, or cortical structures of external events or sensory data are referred to as content and enter into the ventrobasal thalamus at the "specific" thalamic nuclei. These neurons project to layer IV of the cortex. Similarly, nonspecific inputs provide context from internal state of the brain and enter into intralaminar "non-specific" nuclei in the centrolateral thalamus with axons in layers I and VI.Resonant columns
Studies involving manipulation of slices of visual cortex have shown that thalamocortical resonance induces the formation of coherent regions of similar electrical activity in the cortex. These regions are columnar and are physically separated by areas of inhibited cortex between them. This inhibition appears to be the result of stimulation of the cortical white matterWhite matter
White matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
afferents specifically at the gamma-band frequency and is an active inhibition: administration of a GABAA blocker stops the effect.
Temporal binding
Thalamocortical resonance is thought to potentially explain coherence of perception in the brain. Temporal coincidence could occur in this way through the integration of both specific and non-specific thalamic nuclei synapsing on apical dendrites of cortical pyramidal cells. Resonance is thus established as the pyramidal neurons feed back into the thalamus. This process is taking place simultaneously across many different loops throughout the cortex during conscious perception - it is this ability to support synchronized events between remote brain regions that may provide for coherent perception. In this system as proposed, the specific neurons in the thalamus serve to introduce sensory input to a self-sustained feedback loop that is modulated by the non-specific cells relaying information about the context, or internal state of cognition.Brain state
MagnetoencephalographyMagnetoencephalography
Magnetoencephalography is a technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using arrays of SQUIDs...
(MEG) has been used to show that during conscious perception, gamma-band frequency electrical activity and thalamocortical resonance occurs in the human brain. Sensory input can be seen to modulate the oscillatory patterns of this activity while awake. 40 Hz oscillation is also seen during REM sleep, but interestingly auditory input does not appear to induce any changes during this sleep state. It appears then that sensory input may be blocked from interfering with the intrinsic state of the brain during REM.
Alpha oscillations and attention
Gamma-range oscillations are not the only rhythms associated with thalamocortical resonance. Alpha frequency oscillations have been noted in the human occipitalOccipital lobe
The occipital lobe is the visual processing center of the mammalian brain containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1...
-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...
cortex. This activity could be generated by pyramidal neurons in layer IV. It has been shown that alpha rhythms seem to be related to the focus of attention: external focus on visual tasks diminish alpha activity while internal focus as in heavy working memory tasks show an increase in alpha magnitudes.
Thalamocortical dysrhythmia
Thalamocortical dysrhythmiaThalamocortical Dysrhythmia
Thalamocortical Dysrhythmia is a theoretical framework in which neuroscientists try to explain the positive and negative symptoms induced by neurological disorders like Parkinson's Disease, neurogenic pain, Tinnitus, Epilepsy as well as neuropsychiatric disorders like depression.In TCD the...
(TCD) is a proposed concept for the disruption of normal gamma-band electrical activity seen between the cortex and thalamic neurons. This state is seen in patients with neuropathic pain
Neuropathic pain
Neuropathic pain results from lesions or diseases affecting the somatosensory system. It may be associated with abnormal sensations called dysesthesia, which occur spontaneously and allodynia that occurs in response to external stimuli. Neuropathic pain may have continuous and/or episodic ...
, tinnitus
Tinnitus
Tinnitus |ringing]]") is the perception of sound within the human ear in the absence of corresponding external sound.Tinnitus is not a disease, but a symptom that can result from a wide range of underlying causes: abnormally loud sounds in the ear canal for even the briefest period , ear...
, and Parkinson’s disease and is characterized by the presence of unusually low-frequency resonance in the thalamocortical system and is associated with disruption of many brain functions including cognition
Cognition
In science, cognition refers to mental processes. These processes include attention, remembering, producing and understanding language, solving problems, and making decisions. Cognition is studied in various disciplines such as psychology, philosophy, linguistics, and computer science...
, sensory perception, and motor control
Motor control
Motor control are information processing related activities carried out by the central nervous system that organize the musculoskeletal system to create coordinated movements and skilled actions...
. TCD occurs when thalamocortical neurons become hyperpolarized, allowing T type calcium channels to activate and the cell’s oscillatory properties to change. A repeated burst of action potentials occurs at lower frequencies in the 4-10 Hz range. These bursts can be sustained by inhibition from the thalamic reticular nucleus and may cause an activation of cortical regions adjacent to the abnormal neurons that are normally inhibited by gamma-band activity. While the effect of the deviation from normal patterns of oscillatory activity in this system is still debatable, it is proposed that the phenomenon can explain chronic pain in cases where there is no peripheral nerve damage.