Thalamocortical dysrhythmia (TCD) is a theoretical framework in which neuroscientists try to explain the positive and negative symptoms induced by neuropsychiatric disorders like

Parkinson's Disease Parkinson's disease (PD), or simply Parkinson's, is a neurodegenerative disease primarily of the central nervous system, affecting both motor system, motor and non-motor systems. Symptoms typically develop gradually and non-motor issues become ...

, neurogenic pain,

tinnitus Tinnitus is a condition when a person hears a ringing sound or a different variety of sound when no corresponding external sound is present and other people cannot hear it. Nearly everyone experiences faint "normal tinnitus" in a completely ...

, visual snow syndrome,

schizophrenia Schizophrenia () is a mental disorder characterized variously by hallucinations (typically, Auditory hallucination#Schizophrenia, hearing voices), delusions, thought disorder, disorganized thinking and behavior, and Reduced affect display, f ...

obsessive–compulsive disorder Obsessive–compulsive disorder (OCD) is a mental disorder in which an individual has intrusive thoughts (an ''obsession'') and feels the need to perform certain routines (''Compulsive behavior, compulsions'') repeatedly to relieve the dis ...

depressive disorder A mood disorder, also known as an affective disorder, is any of a group of conditions of mental disorder, mental and Abnormal behavior, behavioral Disorder (medicine), disorder where the main underlying characteristic is a disturbance in the per ...

and

epilepsy Epilepsy is a group of Non-communicable disease, non-communicable Neurological disorder, neurological disorders characterized by a tendency for recurrent, unprovoked Seizure, seizures. A seizure is a sudden burst of abnormal electrical activit ...

. In TCD, normal thalamocortical resonance is disrupted by changes in the behaviour of

neurons A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

in the thalamus.
TCD can be treated with neurosurgical methods like the central lateral thalamotomy, 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 (MEG) is a functional neuroimaging technique for mapping brain activity by recording magnetic fields produced by electric current, electrical currents occurring naturally in the human brain, brain, using very sensitive magn ...

(MEG), and

electroencephalography Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignal, bio signals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in ...

(EEG) recordings on the scalp as well as local field potential (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 compared to healthy controls. This indicates a close coupling of cortex and thalamus in the generation of the pathological theta rhythmicity. The thalamic loss of input or gated activity allows the frequency of the thalamo-cortical column to slow into the theta or delta band, and this defeats the lateral inhibition, so faster Gamma band activity appears surrounding the area of slower alpha seen in the theta band, with the theta associated with negative symptoms and the Gamma for positive symptoms. This is documented in Tinnitus (phantom sound) and phantom pain, as well as Parkinsonism and recently even in depression (see current work by Dirk DeRidder, MD, PhD). The thalamocoherence was identified by machine learning, with significant differentiation of each of these clinical entities from normal by the presence of the dysrhythmia, and with the specific disorder differentiated by the spatial/topographic networks involved. It was also proposed that

psychotic disorders In psychopathology, psychosis is a condition in which a person is unable to distinguish, in their experience of life, between what is and is not real. Examples of psychotic symptoms are delusions, hallucinations, and disorganized or incoh ...

present in Parkinson disease‐

dementia with Lewy bodies Dementia with Lewy bodies (DLB) is a type of dementia characterized by changes in sleep, behavior change (individual), behavior, cognition, movement, and dysautonomia, regulation of automatic bodily functions. Unlike some other dementias, mem ...

depend on thalamic abnormal rhythms.

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 noninvasive therapy.

Background

Evidence

Therapy

References

Further reading