Thalamocortical dysrhythmia

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, Epilepsy as well as neuropsychiatric disorders like Depression. In TCD the intricate dynamics between thalamus and cerebral cortex are disrupted by changes in the behaviour of neurons 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 5Hz.

Evidence
Evidence for TCD comes from Electroencephalography (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.

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.