Neural Encoding of Felt and Imagined Touch Within Human Posterior Parietal Cortex

Abstract

In the human posterior parietal cortex (PPC), single units encode high-dimensional information with partially mixed representations that enable small populations of neurons to encode many variables relevant to movement planning, execution, cognition, and perception. Here we test whether a PPC neuronal population previously demonstrated to encode visual and motor information is similarly selective in the somatosensory domain. We recorded from 1423 neurons within the PPC of a human clinical trial participant during objective touch presentation and during tactile imagery. Neurons encoded experienced touch with bilateral receptive fields, organized by body part, and covered all tested regions. Tactile imagery evoked body part specific responses that shared a neural substrate with experienced touch. Our results are the first neuron level evidence of touch encoding in human PPC and its cognitive engagement during tactile imagery which may reflect semantic processing, sensory anticipation, and imagined touch.

Cognition through internal models: Mirror neurons as one manifestation of a broader mechanism

“…First, the neural populations that underly our putative internal models are consistent with grounded or embodied notions of cognition. The tactile responses in the current study have parametrically encoded tactile receptive fields that activate within 60ms of physical contact (28), consistent with a bottom-up (sensory-driven) role in tactile processing. These responses can be contrasted with the highlyselective and long-latency (260-400ms) responses reported for "concept cells" within the medial temporal lobe (29).…”

“…We recorded populations of single neurons from a microelectrode array implanted in participant NS, a tetraplegic individual (spinal injury at cervical levels 3–4; C3/4) participating in a clinical brain-machine interface study (Fig S1). NS had well-defined sensory receptive fields that responded at short (~60ms) latencies suggesting a role in the bottom-up sensory processing ( 19 ). Such responses opened the possibility of studying mirror-like phenomena in the sensory domain.…”

“…These responses can be contrasted with the highly-selective and long-latency (260-400ms) responses reported for “concept cells” within the medial temporal lobe ( 29 ). The fact that tactile imagery ( 28 ) and observation engage sensory-like populations suggests that tactile cognition is intricately tied to our somatosensory experiences and argues against purely “symbolist” views of cognition ( 30 ). These tactile responses are likely not raw representations of sensory inputs: neural responses in anterior regions of the PPC are consistent with state estimators that compensate for sensory delays and merge visual and somatosensory inputs ( 31, 32 ).…”

“…We have recently recorded populations of single neurons in the human posterior parietal cortex (PPC) during motor, sensory, and cognitive behaviors. These neurons encode many diverse bodyrelated variables such as action verbs, observed actions, motor and sensory imagery, and motor plans (18)(19)(20)(21). Individual neurons are often complex, yet population-level representations demonstrate generalizable encoding across these varied domains in a functional organization we termed partially-mixed selectivity (20).…”

Exploring Cognition with Brain–Machine Interfaces

“…Whereas sensation above the injury is preserved and can be explored by interactions between the participants, the experimenter, and the environment, sensations below the injury must be elicited by alternative methods. For example, intracortical microstimulation to S1 can elicit naturalistic percepts (Armenta , Fifer et al 2020, Flesher et al 2016, and performing somatosensory imagery-the vivid recall of previously experienced sensations-can elicit neurophysiological responses specific to the sensations being imagined (Bashford et al 2021, Chivukula et al 2021.…”