Two whisker motor areas in the rat cortex: Evidence from thalamocortical connections

Abstract

In primates, the motor cortex consists of at least seven different areas, which are involved in movement planning, coordination, initiation, and execution. However, for rats, only the primary motor cortex has been well described. A rostrally located second motor area has been proposed, but its extent, organization, and even definitive existence remain uncertain. Only a rostral forelimb area (RFA) has been definitively described, besides few reports of a rostral hindlimb area. We have previously proposed existence of a second whisker area, which we termed the rostral whisker area (RWA), based on its differential response to intracortical microstimulation compared with the caudal whisker area (CWA) in animals under deep anesthesia (Tandon et al. [2008] Eur J Neurosci 27:228). To establish that RWA is distinct from the caudally contiguous CWA, we determined sources of thalamic inputs to the two proposed whisker areas. Sources of inputs to RFA, caudal forelimb area (CFA), and caudal hindlimb region were determined for comparison. The results show that RWA and CWA can be distinguished based on differences in their thalamic inputs. RWA receives major projections from mediodorsal and ventromedial nuclei, whereas the major projections to CWA are from the ventral anterior, ventrolateral, and posterior nuclei. Moreover, the thalamic nuclei that provide major inputs to RWA are the same as for RFA, and the nuclei projecting to CWA are same as for CFA. The results suggest that rats have a second rostrally located motor area with RWA and RFA as its constituents.

Transformation of Perception from Sensory to Motor Cortex

“…In the remainder of this article, we examine neuronal activity in behaving rats from two regions (Figure S4)—vS1, the main entryway of sensory signals to the cerebral cortex [11, 12], and vM1, the target of projections from sensory cortical regions and a source of dense projections to major motor output systems [13, 14]. To elucidate the overall profile of firing, Figures 4A and 4B show the peristimulus time histograms (PSTHs) constructed from the pooled activity of single and multiunits from vS1 and vM1, respectively.…”

“…Similarly, in the present work, vS1 responses were characterized by a local timescale (Figures 5E and 5F). In vM1, a principal vS1 target in frontal cortex [13, 14], neuronal responses failed to show robust local coding; instead, they varied in relation to stimulus mean speed as well as in relation to stimulus duration. Firing rates in vM1 population did not “ramp up” along the course of stimulus 1 (Figure 4B), yet the population assumed a duration-dependent state immediately after termination of the vibration and maintained this state throughout the interstimulus delay (Figures 7C and 7D).…”

High‐order motor cortex in rats receives somatosensory inputs from the primary motor cortex via cortico‐cortical pathways

“…Therefore, it is possible that learning-related plastic changes in M1 (CFA) also cause successive changes in M2 (RFA) neuronal activity during the acquisition of skilled forelimb movements. In addition to inputs from the CFA, the RFA receives inputs from the cerebellum via the ventral anterior-lateral complex of the thalamus (Kuramoto et al, 2009;Mohammed & Jain, 2014). The cerebello-thalamo-cortical circuit has been implicated in a variety of sensorimotor functions, including somatosensory integration (Manzoni, 2007), the control of continuous movements and externally guided movements (Elsinger et al, 2006;Schnitzler et al, 2006;Lewis et al, 2007).…”

“…In an anatomical sense, the CFA and RFA in rats are considered to be analogous to the primary motor cortex and the premotor and/or supplementary motor cortices, respectively, in primates (Rouiller et al ., ; Wang & Kurata, ; Mohammed & Jain, ). Consistent with this hypothesis, the RFA modulates descending output signals from the CFA but the CFA does not modulate signals from the RFA (Deffeyes et al ., ).…”

Cortical Reorganization of Sensorimotor Systems and the Role of Intracortical Circuits After Spinal Cord Injury

“…Cortical motor maps are shaped through the anatomical refinement of cortical output [4] as well as the strengthening of intrinsic connectivity [5]. The primary motor cortex (M1) exhibits extensive intrinsic connectivity [6][7][8] in addition to topographic connections with a myriad of cortical and subcortical targets [9][10][11][12][13][14].…”