Somatosensory system

About: Somatosensory system is a research topic. Over the lifetime, 6371 publications have been published within this topic receiving 316900 citations.

Value-guided remapping of sensory cortex by lateral orbitofrontal cortex.

Abstract: Adaptive behaviour crucially depends on flexible decision-making, which in mammals relies on the frontal cortex, specifically the orbitofrontal cortex (OFC)1–9. How OFC encodes decision variables and instructs sensory areas to guide adaptive behaviour are key open questions. Here we developed a reversal learning task for head-fixed mice, monitored the activity of neurons of the lateral OFC using two-photon calcium imaging and investigated how OFC dynamically interacts with primary somatosensory cortex (S1). Mice learned to discriminate ‘go’ from ‘no-go’ tactile stimuli10,11 and adapt their behaviour upon reversal of stimulus–reward contingency (‘rule switch’). Imaging individual neurons longitudinally across all behavioural phases revealed a distinct engagement of S1 and lateral OFC, with S1 neural activity reflecting initial task learning, whereas lateral OFC neurons responded saliently and transiently to the rule switch. We identified direct long-range projections from lateral OFC to S1 that can feed this activity back to S1 as value prediction error. This top-down signal updated sensory representations in S1 by functionally remapping responses in a subpopulation of neurons that was sensitive to reward history. Functional remapping crucially depended on top-down feedback as chemogenetic silencing of lateral OFC neurons disrupted reversal learning, as well as plasticity in S1. The dynamic interaction of lateral OFC with sensory cortex thus implements computations critical for value prediction that are history dependent and error based, providing plasticity essential for flexible decision-making. Dynamic interaction of neurons in lateral orbitofrontal cortex with the sensory cortex implements value-prediction computations that are history dependent and error based, providing plasticity essential for flexible decision-making.

Ipsilateral hand input to area 3b revealed by converging hemodynamic and electrophysiological analyses in macaque monkeys.

Abstract: Functional magnetic resonance imaging (fMRI) of the hand representation in primary somatosensory cortex (area 3b) of macaque monkeys revealed an ipsilateral hand input undetected by most previous studies. Ipsilateral responses had a hemodynamic signature indistinguishable from that of contralateral hand responses. We explored the neural mechanisms of the fMRI effects using a second derivative analysis of field potentials [current source density (CSD) analysis] combined with action potential profiles, sampled from area 3b using linear array multielectrodes. In contrast to the predominantly excitatory contralateral response, the colocated ipsilateral response appeared dominated by inhibition, suggesting that ipsilateral inputs may have modulatory effects on contralateral input processing. Our findings confirm bimanual convergence at the earliest stage of cortical somatosensory processing in primates. They also illustrate the value of combined CSD and fMRI analyses in monkeys for defining hidden aspects of sensory function and for investigating the neuronal processes generating fMRI signals.

Differential effects of GABA and bicuculline on rapidly- and slowly-adapting neurons in primary somatosensory cortex of primates

Abstract: In cortical area 3b of monkeys, responses of 71 single neurons to controlled indentations of glabrous skin were recorded before and during iontophoretic application of GABA and bicuculline methiodide (BMI), a GABA receptor antagonist. Constant amplitude indentations were applied to selected sites within the receptive fields of neurons representing the glabrous skin on the digits and palm. Profiles of response magnitudes across stimulation sites were used to quantify receptive field dimensions before and during antagonism of GABAergic inhibition. During administration of BMI, the receptive fields of 26 rapidly-adapting neurons were increased by 3–4 times their original size. Response latencies were substantially longer in the region of expansion than in the original receptive field, suggesting that expansion might be mediated by intracortical connections. The expansion of RFs onto adjacent digits after blockade of GABAergic inhibition suggests that somatotopic reorganization following digit amputations may be subserved by existing excitatory connections. The responses of slowly-adapting neurons were separated into two components, a “dynamic” response corresponding to activity elicited by the initial indenting ramp and a “static” response produced by the sustained indentation. Among 8 slowly-adapting neurons tested with BMI, the receptive fields of the dynamic response component increased to an extent that was similar to the change produced in rapidly-adapting neurons. By contrast, the static response component was rarely altered by BMI. Comparison of the responses to administration of GABA revealed that only 12 of 27 slowly-adapting neurons were inhibited in a dose-dependent manner, whereas 37 of 44 rapidly-adapting neurons exhibited significant reduction of responses in the presence of GABA. Hypotheses are proposed to explain the differential effect of BMI and GABA on slowly- and rapidly-adapting cortical neurons.