Ipsilateral cortical inputs to the rostral and caudal motor areas in rats

Abstract

Rats have a complete body representation in the primary motor cortex (M1). Rostrally there are additional representations of the forelimb and whiskers, called the rostral forelimb area (RFA) and the rostral whisker area (RWA). Recently we showed that sources of thalamic inputs to RFA and RWA are similar, but they are different from those for the caudal forelimb area (CFA) and the caudal whisker area (CWA) of M1 (Mohammed and Jain [2014] J Comp Neurol 522:528-545). We proposed that RWA and RFA are part of a second motor area, the rostral motor area (RMA). Here we report ipsilateral cortical connections of whisker representation in RMA, and compare them with connections of CWA. Connections of RFA, CFA, and the caudally located hindlimb area (CHA), which is a part of M1, were determined for comparison. The most distinctive features of cortical inputs to RWA compared with CWA include lack of inputs from the face region of the primary somatosensory cortex (S1), and only about half as much inputs from S1 compared with the lateral somatosensory areas S2 (second somatosensory area) and the parietal ventral area (PV). A similar pattern of inputs is seen for CFA and RFA, with RFA receiving smaller proportion of inputs from the forepaw region of S1 compared with CFA, and receiving fewer inputs from S1 compared with those from S2. These and other features of the cortical input pattern suggest that RMA has a distinct, and more of integrative functional role compared with M1. J. Comp. Neurol. 524:3104-3123, 2016. © 2016 Wiley Periodicals, Inc.

The role of forelimb motor cortex areas in goal directed action in mice

“…In rodents, two frontal cortical regions are critically involved in controlling the contralateral forelimb: the rostral forelimb area (RFA) and the caudal forelimb area (CFA). They have been identified by electrical 17 – 20 and optogenetic microstimulation 21 , 22 , as well as by anatomical tracings 23 – 25 , yet their respective functional role is still unclear. It has been speculated that they are organized in an analogous way to the primate frontal cortex 17 , 19 , 23 , 26 – 28 with CFA as the primary motor cortex and RFA as a premotor area.…”

Differential effects of open- and closed-loop intracortical microstimulation on firing patterns of neurons in distant cortical areas

“…To model a relevant system in vivo, the rostral forelimb area (RFA), a premotor area, was used for neural recordings while either closed-loop ADS or random stimulation (RS) was delivered to somatosensory cortex (S1), either in the S1 forelimb area (S1FL) or the S1 barrel field (S1BF). These areas share reciprocal neuroanatomical connections, providing an anatomical framework for changing synaptic efficacy [29]. In a previous study, we found that an ADS protocol in a chronic injury model, i.e., pairing the occurrence of spikes in RFA with ICMS applied to S1, led to increased firing within RFA over a period of several days [28].…”

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

“…CFA, which reorganizes during skilled motor learning [17], exhibits significantly greater input from the primary somatosensory cortex and less from the secondary somatosensory cortex than RFA (Fig. 4) [10]. Physiological studies in the rat also suggest that RFA lacks sensory inputs, in contrast to CFA [155].…”

“…Motor intrinsic connections dictate the selection of movement-related muscle synergies through functional linking of motor cortical points, lateral inhibition of competing output, and shaping of representational borders [130][131][132][133][134]. Physiological and anatomical studies have illuminated the extensive intrinsic connections within the primary motor cortex [6][7][8] as well as the intracortical connections to higher motor areas [135][136][137], somatosensory cortex [10,138,139], and other cortical areas involved in motor control and spatial awareness (i.e., posterior parietal cortex, prefrontal cortex, and retrosplenial cortex) [10,[139][140][141][142]. Horizontal circuits interconnect neurons in the cortical columns within and across cortical regions, comprising a network of horizontally projecting axons in layers 2/3 and 5 [143,144].…”

“…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].…”