Thalamocortical functions

Thalamocortical code conversion

Our studies revealed that thalamic “relay” nuclei are not mere relays. Rather, they process sensory information.

One nucleus we focused on is the POm – a vibrissal-recepient sector in the posterior nucleus. We showed that POm neurons can be shifted from an OR-like response mode to an AND-like response mode.Such a shift can be controlled by the motor cortex via a dis-inhibitory pathway through the zona incerta (ZI), induced by a consistent sensory input, or modulated by state-dependent neuromodulatory systems.

 

Thalamocortical coding

We examined the coding schemes occurring at the first forebrain level that receives inputs necessary for generating such internal representations – the thalamocortical network. Single units were recorded in eight thalamic and cortical stations in artificially whisking anesthetized rats.

Neuronal representations of object location generated across these stations and expressed in response latency and magnitude were classified based on graded and binary coding schemes. Both graded and binary coding schemes occurred across the entire thalamocortical network, with a general tendency of graded-to-binary transformation from thalamus to cortex. Overall, 63% of the neurons of the thalamocortical network coded object position in their firing.

Thalamocortical responses exhibited a slow dynamics during which the amount of coded information increased across 4-5 cycles of artificial whisking and then stabilized. Taken together, the results indicate that the thalamocortical network contains dynamic mechanisms that can converge over time on multiple coding schemes of object location, schemes which essentially transform temporal coding to rate coding and gradual to labeled-line coding.
 

Relevant papers

 

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