An analysis of the interaction of the parietal and visual regions of the cortex with the posterior lateral nucleus of the thalamus]

Cooling and ablation of the parietal associative (P) and primary visual projection (VI) areas in nembutalized cats revealed facilitating and inhibitory descending influences of the above areas on the postero-lateral nucleus (LP) of the ipsilateral thalamus where visual signals generate an early specific and a late unspecific components of heterogenous evoked responses. Unidirectional influences activating the early component and fully controlling the appearance and course of the late component are more manifest in P which is a part of the same associative brain system as LP; they are less manifest in VI which belongs to the projection system. At later cooling stages the centrifugal influences of P and VI are sometimes of opposite signs; this effect is connected with reciprocal relations between projection and association systems and processes or selfcontrol within the association system. The corticofugal effects also participate in the common activity of P and VI taking place to a certain degree at the level of the LP which activates these cortical structures.