Sensory computations in the cuneate nucleus of macaques

Abstract

Tactile nerve fibers fall into a few classes that can be readily distinguished based on their spatiotemporal response properties. Because nerve fibers reflect local skin deformations, they individually carry ambiguous signals about object features. In contrast, cortical neurons exhibit heterogeneous response properties that reflect computations applied to convergent input from multiple classes of afferents, which confer to them a selectivity for behaviorally relevant features of objects. The conventional view is that these complex response properties arise within the cortex itself, implying that sensory signals are not processed to any significant extent in the two intervening structures—the cuneate nucleus (CN) and the thalamus. To test this hypothesis, we recorded the responses evoked in the CN to a battery of stimuli that have been extensively used to characterize tactile coding in both the periphery and cortex, including skin indentations, vibrations, random dot patterns, and scanned edges. We found that CN responses are more similar to their cortical counterparts than they are to their inputs: CN neurons receive input from multiple classes of nerve fibers, they have spatially complex receptive fields, and they exhibit selectivity for object features. Contrary to consensus, then, the CN plays a key role in processing tactile information.

Emergence of a somatosensory tonotopic map for substrate vibration in the brainstem

“…3). This was consistent with the electrophysiological mapping of receptive fields in the previous literature 17,18 .…”

The encoding of touch by somatotopically aligned dorsal column subdivisions

“…Somatosensory coding in DCN neurons is heterogeneous 18 – 21 , but how tactile signals are organized within the DCN and distributed to downstream targets remains unknown. Using mice, we sought to determine how sensory representations of the hindlimb are encoded at this early stage of the somatosensory hierarchy.…”

Mechanoreceptor signal convergence and transformation in the dorsal horn flexibly shape a diversity of outputs to the brain

“…Contrary to the classic view of segregated mechanosensory modalities, recent studies indicate that tactile responses in S1 reflect subcortical convergence of Aβ LTMR subtype signals (Emanuel et al, 2021; Pei et al, 2009; Suresh et al, 2021). Evidence for Aβ LTMR signal integration has also been observed in the DCN and somatosensory thalamus (Emanuel et al, 2021; Suresh et al, 2021).…”

“…Contrary to the classic view of segregated mechanosensory modalities, recent studies indicate that tactile responses in S1 reflect subcortical convergence of Aβ LTMR subtype signals (Emanuel et al, 2021; Pei et al, 2009; Suresh et al, 2021). Evidence for Aβ LTMR signal integration has also been observed in the DCN and somatosensory thalamus (Emanuel et al, 2021; Suresh et al, 2021). Neurons in the macaque DCN, for example, exhibit spatially complex RFs, intermediate rates of adaptation to sustained skin indentation, and orientation tuning, which likely reflect mixing of Aβ LTMR subtype inputs (Suresh et al, 2021).…”

“…Evidence for Aβ LTMR signal integration has also been observed in the DCN and somatosensory thalamus (Emanuel et al, 2021; Suresh et al, 2021). Neurons in the macaque DCN, for example, exhibit spatially complex RFs, intermediate rates of adaptation to sustained skin indentation, and orientation tuning, which likely reflect mixing of Aβ LTMR subtype inputs (Suresh et al, 2021). Thus, the emerging view is that signals from physiologically diverse mechanosensory neurons converge early in the somatosensory hierarchy to generate complex tactile feature representations.…”