Modulation of tuning properties of thalamic relay neurons by corticothalamic 'feedback' projections in rats

This thesis is aimed at developing a better understanding of the cortical influence on computational maps at subcortical levels by studying how cortex modulates the tuning properties of thalamic relay neurons using rat's vibrissa system as the model system. Firstly by examining the interhemispheric interaction in rat's vibrissa system, studies in this dissertation demonstrated that one barrel field cortex (BFC) could modulate neural responses in contralateral homotopic BFC in an activity-dependent manner. Then by investigating the interaction between the bilateral integration and corticothalamic feedback, studies further demonstrated that the ipsilateral corticothalamic feedback pathway is influenced indirectly by contralateral, as well as ipsilateral cortical areas. The influence can act through mechanisms that regulate the response threshold of thalamic relay neurons to test stimuli. And we advanced our understanding of the corticothalamic system further by showing that cortical modulation could operate precisely on one specific parameter: the angular tuning map, in a way caters to the preference of cortex. These effects could result in a magnifying/minifying effect on the tuning maps by temporarily and reversibly increasing or decreasing the sensitivity to certain stimuli or enlarging/shrinking the information representation area in the thalamus. And finally we propose that the active modulation of tuning maps by cortex might be achieved through changing of synaptic efficacy which is related to the spike-timing-dependent-plasticity (STDP).