Characteristics of synaptic connections between rodent primary somatosensory and motor cortices

Abstract

The reciprocal connections between primary motor (M1) and primary somatosensory cortices (S1) are hypothesized to play a crucial role in the ability to update motor plans in response to changes in the sensory periphery. These interactions provide M1 with information about the sensory environment that in turn signals S1 with anticipatory knowledge of ongoing motor plans. In order to examine the synaptic basis of sensorimotor feedforward (S1-M1) and feedback (M1-S1) connections directly, we utilized whole-cell recordings in slices that preserve these reciprocal sensorimotor connections. Our findings indicate that these regions are connected via direct monosynaptic connections in both directions. Larger magnitude responses were observed in the feedforward direction (S1-M1), while the feedback (M1-S1) responses occurred at shorter latencies. The morphology as well as the intrinsic firing properties of the neurons in these pathways indicates that both excitatory and inhibitory neurons are targeted. Differences in synaptic physiology suggest that there exist specializations within the sensorimotor pathway that may allow for the rapid updating of sensory-motor processing within the cortex in response to changes in the sensory periphery.

Imaging the Spatio-Temporal Dynamics of Supragranular Activity in the Rat Somatosensory Cortex in Response to Stimulation of the Paws

“…These observations represent the functional counterpart of the known anatomical projections from the somatosensory to the motor cortex [17], [37]–[41]. Within the sensorimotor cortex, the barrel cortex displays the maximal separation between sensory and motor [36], and somatosensory stimuli first activate the somatosensory cortex and then the motor cortex [17], [40].…”

“…Second, the forepaw somatosensory cortex is mostly separated from the corresponding region of the motor cortex, whereas most of the hindpaw somatosensory cortex overlaps with the corresponding region of the motor cortex [35], [36]. Because of the known projections from the somatosensory cortex to the motor cortex [17], [37]–[41], it therefore seems reasonable to hypothesize that the spatio-temporal dynamics of supragranular cortical activation in response to stimulation of the forepaw compared to stimulation of the hindpaw will be different.…”

Assessment of gait and sensorimotor deficits in the D1CT-7 mouse model of Tourette syndrome

“…This characteristic appears to be phenomenologically similar to the recently-reported reduction in GABAergic inhibitory tone in the somatosensory cortex of TS patients (Puts et al, 2015). The link between somatosensory cortex hyperactivation and gait deficits is supported by at least two lines of evidence: first, the neurons in this area exert a strong inhibitory influence on motor cortex neurons (Rocco-Donovan et al, 2011); second, their firing patterns are synchronized with swing and stance phases of the locomotor stride cycle (Favorov et al, 2015). …”

The influence of sensory afferent input on local motor cortical excitatory circuitry in humans

“…The primary motor cortex receives strong monosynaptic inputs from the primary sensory cortex (Rocco‐Donovan et al . ). Inactivation of these inputs causes disruption of motor acts such as fine motor coordination, sustained muscle contractions and appropriate grip force (Hikosaka et al .…”