Thalamocortical Dysrhythmia (TCD) 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

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...

, Epilepsy

Epilepsy

Epilepsy is a common chronic neurological disorder characterized by seizures. These seizures are transient signs and/or symptoms of abnormal, excessive or hypersynchronous neuronal activity in the brain.About 50 million people worldwide have epilepsy, and nearly two out of every three new cases...

 as well as neuropsychiatric disorders like depression.

In TCD the intricate dynamics between 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 cerebral cortex

Cerebral cortex

The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...

 are disrupted by changes in the behaviour of neurons in the thalamus.

TCD can be treated with neurosurgical

Neurosurgery

Neurosurgery is the medical specialty concerned with the prevention, diagnosis, treatment, and rehabilitation of disorders which affect any portion of the nervous system including the brain, spine, spinal cord, peripheral nerves, and extra-cranial cerebrovascular system.-In the United States:In...

 methods like the central lateral thalamotomy

Thalamotomy

First introduced in the 1950s, thalamotomy is an invasive procedure, primarily effective for tremors such as those associated with Parkinson's Disease , where a selected portion of the thalamus is surgically destroyed...

, which due to its invasiveness is only used on patients that have proven resistant to conventional therapies.

Background

At the base of the theory lies diminished excitatory or increased inhibitory input at the thalamic level. This leads to a switch of the thalamocortical neurons from tonic to burst firing and subsequently entrains thalamic and cortical areas with pathological oscillations at around 5 Hz.

Evidence

Evidence for TCD comes from Magnetoencephalography

Magnetoencephalography

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), and Electroencephalography

Electroencephalography

Electroencephalography is the recording of electrical activity along the scalp. EEG measures voltage fluctuations resulting from ionic current flows within the neurons of the brain...

 (EEG) recordings on the scalp as well as local field potential

Local field potential

A local field potential is a particular class of electrophysiological signals, which is dominated by the electrical current flowing from all nearby dendritic synaptic activity within a volume of tissue. A voltage is produced by the summed synaptic current flowing across the resistance of the local...

 (LFP) recordings in the patients' thalamus during surgery. Analysing the power spectra reveals increased coherence as well as increased bicoherence in the power spectra in the theta band

Theta rhythm

A theta rhythm is an oscillatory pattern in EEG signals recorded either from inside the brain or from electrodes glued to the scalp. Two types of theta rhythm have been described...

 compared to healthy controls. This indicates a close coupling of cortex and thalamus in the generation of the pathological theta rhythm

Theta rhythm

A theta rhythm is an oscillatory pattern in EEG signals recorded either from inside the brain or from electrodes glued to the scalp. Two types of theta rhythm have been described...

icity.

Therapy

While it is not clear how this happens in detail, surgical intervention by means of lesioning small parts of the central lateral thalamic areas has proven successful as a therapy for Parkinson's Disease as well as neurogenic pain.

Neurofeedback, where the brain is trained to emphasise and de-emphasise brain wave frequencies, amplitudes and coherence can be an effective non invasive therapy.