Fig. 5.

The central medial (i.e. non-specific) nucleus of the thalamus is functionally connected to specific and reticular thalamic nuclei. Shown are experimental results from Purpura and Cohen (Purpura and Cohen, 1962). (A) Experimental preparation. In vivo experiments were performed in the cat. The central medial (CM) nucleus was stimulated with an extracellular stimulating electrode. Responses to such stimulation were recorded in neurons of the ventromedial (VM) using intracellular recording pipettes. Thalamic structures that are likely involved in the VM neuron responses are filled in with red, blue or green. (B) An example, intracellular recording of a VM neuron. Each red arrowhead represents a single electrical stimulus delivered to CM. Prior to CM stimulation, action potentials are spontaneously generated by the VM neuron. The first electrical stimulus elicits a putative excitatory postsynaptic potential (EPSP, blue) with a short latency in the recorded neuron. The putative EPSP is followed by a longer latency inhibitory postsynaptic potential (IPSP, green). Purpura and Cohen speculated that rapid EPSP occurred as a result of direct, monosynaptic connectivity between CM and VM nuclei. The IPSP, in contrast, likely resulted from an indirect, disynaptic connection that initially involved excitation of GABAergic neurons of the reticular thalamic (RT) nucleus, followed by RT-mediated inhibition of VM neurons. This EPSP-IPSP combination is observed to differing extents with subsequent CM stimulation. Following CM stimulation (i.e. stim. end) results in a phase of slow VM neuron depolarization. Resumption of CM stimulation again evokes the EPSP-IPSP combination.