Figure 5.

Location of VL neurons and identification of TCs. (A) The recording site in cat A is shown on a photomicrograph of a parasagittal section of the thalamus. It was located in the rostral VL. The arrow points to the electrolytic lesion mark and the darkened area of tissue filled with WGA-HRP. The site is ∼2 mm caudally to the Nucleus caudatus (NC) of the basal ganglia. (B) The recording site in cat B is shown on a photomicrograph of a coronal section of the thalamus. It was positioned in the middle of the VL. The arrow points to the electrolytic lesion mark and darkened area where fluorescent beads were deposited. The caudal part of putamen (PU), a landmark for the anterior-posterior position of the section, is seen laterally. (C) The recording site in cat C is shown on a photomicrograph of a coronal section of the thalamus. It was positioned in the caudal VL. The arrows point to a track from a reference electrode. The most rostral aspect of the lateral geniculate body (LG), a landmark for the anterior-posterior position of the section, is visible laterally. (A–C) 50 μm thick sections, cresyl violet stain. (D) A photograph of the dorsal surface of the left frontal cortex of cat B. Entrance points of stimulation electrodes into the precruciate sulcus are schematically shown by black dots. Electrodes were placed in the paw (the motor cortex distal forelimb representation, MCd), the elbow and shoulder representations (the motor cortex proximal forelimb representation, MCp) as determined by multiunit recording and micro-stimulation procedures. Cru, cruciate sulcus; Pcd, post-cruciate dimple; mAns, medial ansate sulcus. (E) A collision test determined whether a neuron response was antidromic. Stimulation of the MC evoked a spike in the neuron with a latency of 0.8 ms. To determine whether this spike was elicited antidromically, on a next trial a spontaneous spike of the neuron was used to trigger MC stimulation with 0.4 ms delay. Stimulation delivered with a delay smaller than the time needed for a spontaneous spike to reach the site of stimulation (that is approximately equal to the latent time of an antidromic spike) was not followed by a response. This indicated a collision of ortho- and antidromically conducted spikes and confirmed the antidromic nature of the evoked spike. (F) A reconstruction of positions of individual neurons recorded during locomotion in cats A, B, and C. ■, Purple squares show neurons with somatosensory receptive fields on the shoulder: responding to passive movements in the shoulder joint and/or palpation of muscles on the back or neck; ♦, Yellow diamonds show cells that were activated by movements in the elbow; ▲, Red triangles represent neurons with receptive fields on the wrist or paw. Filled symbols represent neurons with axonal projections to the MC (thalamo-cortical neurons, TCs); open symbols represent neurons whose projections were not identified. Abbreviations: AV, nucleus anterio-ventralis thalami; CI, capsula interna; CL, nucleus centralis lateralis; CLA, claustrum; EPN, nucleus entopeduncularis; LA, nucleus lateralis anterior; LG, lateral geniculate nucleus; LME, lamina medullaris externa thalami; LP, nucleus lateralis posterior; NC, nucleus caudatus; OT, optic tract; PC, pedunculus cerebri; PU, putamen; RE, nucleus reticularis thalami; SUB, nucleus subthalamicus; VA, nucleus ventralis anterior; VL, nucleus ventralis lateralis; VM, nucleus medialis; VPL, nucleus ventralis postero-lateralis; VPM, nucleus ventralis postero-medialis (Adapted with modifications from Marlinski et al., 2012a).