Plasticity, neuronal synchrony and multi-stability in the human thalamus
The brain is an assembly of neurons constantly in flux. Episodes of coordinated activity are thought to be a fundamental mechanism underlying various processes and functions. One such example is illustrated by the synchronization of activity expressed as oscillations, which have been associated with a wide variety of behaviors from the sensory and motor system to decision making and consciousness itself. It is no wonder then that aberrent rhythms have been associated with a range of neurological as well as neuropsychiatric disorders. The use of targeted electrical stimulation to push a system from a pathologically hypersynchronized to an appropriately synchronized state has been reported in many disorders such as Parkinson’s disease, tinnitus, and epilepsy. However, in Tourette syndrome subjects receiving deep brain stimulation (DBS) therapy, the opposite effect has been observed, where the stable state is pushed from pathological hyposynchrony to a more coordinated state.1 This occurs in a nonlinear fashion with multiple stable states appearing over time correlated with different levels of neuronal synchrony. While various theories exist concerning the mechanism of action of DBS, the prominent theory is that of a neuromodulatory effect.2 Degree of neuromodulation and synaptic drive are known to allow the occurrence of switching between multiple stable states. The effect of DBS on pathophysiological molecular and cellular elements which control spike-timing dependent plasticity is explored.
Maling, N.*, Hashemiyoon, R.*, Foote, K., Okun, M., Sanchez, J. C. (2012) Deep brain stimulation for Tourette syndrome leads to increased thalamic gamma power and reduction of tics. PLoS ONE 7(9): e44215.
McIntyre, C. C., Savasta, M., Kerkerian-Le Goff, L., Vitek, J. L. (2004) Uncovering the mechanism(s) of action of deep brain stimulation: activation, inhibition, or both. Clinical Neurophysiology 115 (6): 1239-48.