A neural surveyor to map touch on the body

Perhaps the most recognizable sensory map in all of neuroscience is the somatosensory homunculus. Although it seems straightforward, this simple representation belies the complex link between an activation in a somatotopic map and the associated touch location on the body. Any isolated activation is spatially ambiguous without a neural decoder that can read its position within the entire map, but how this is computed by neural networks is unknown. We propose that the somatosensory system implements multilateration, a common computation used by surveying and global positioning systems to localize objects. Specifically, to decode touch location on the body, multilateration estimates the relative distance between the afferent input and the boundaries of a body part (e.g., the joints of a limb). We show that a simple feedforward neural network, which captures several fundamental receptive field properties of cortical somatosensory neurons, can implement a Bayes-optimal multilateral computation. Simulations demonstrated that this decoder produced a pattern of localization variability between two boundaries that was unique to multilateration. Finally, we identify this computational signature of multilateration in actual psychophysical experiments, suggesting that it is a candidate computational mechanism underlying tactile localization.

Organization of the inputs and outputs of the mouse superior colliculus

The superior colliculus (SC) receives diverse and robust cortical inputs to drive a range of cognitive and sensorimotor behaviors. However, it remains unclear how descending cortical input arising from higher-order associative areas coordinate with SC sensorimotor networks to influence its outputs. Here, we construct a comprehensive map of all cortico-tectal projections and identify four collicular zones with differential cortical inputs: medial (SC.m), centromedial (SC.cm), centrolateral (SC.cl) and lateral (SC.l). Further, we delineate the distinctive brain-wide input/output organization of each collicular zone, assemble multiple parallel cortico-tecto-thalamic subnetworks, and identify the somatotopic map in the SC that displays distinguishable spatial properties from the somatotopic maps in the neocortex and basal ganglia. Finally, we characterize interactions between those cortico-tecto-thalamic and cortico-basal ganglia-thalamic subnetworks. This study provides a structural basis for understanding how SC is involved in integrating different sensory modalities, translating sensory information to motor command, and coordinating different actions in goal-directed behaviors.

Explanation Within Arm’s Reach: A Predictive Processing Framework for Single Arm Use in Octopuses

Octopuses are highly intelligent animals with vertebrate-like cognitive and behavioural repertoires. Despite these similarities, vertebrate-based models of cognition and behaviour cannot always be successfully applied to octopuses, due to the structural and functional characteristics that have evolved in their nervous system in response to the unique challenges posed by octopus morphology. For instance, the octopus brain does not support a somatotopic or point-for-point spatial map of the body—an important feature of vertebrate nervous systems. Thus, while octopuses are capable of motor tasks whose vertebrate counterparts require detailed interoceptive monitoring, these movements may not be explainable using motor control frameworks premised on internal spatial representation. One such motor task is the extension of a single arm. The ability of octopuses to select and use a single arm without the guidance of a somatotopic map has been regarded as a motor control puzzle. In an attempt at a solution, this paper develops a predictive processing account of single-arm extension in octopuses.

Neuronal Circuits in Barrel Cortex for Whisker Sensory Perception

The array of whiskers on the snout provides rodents with tactile sensory information relating to the size, shape and texture of objects in their immediate environment. Rodents can use their whiskers to detect stimuli, distinguish textures, locate objects and navigate. Important aspects of whisker sensation are thought to result from neuronal computations in the whisker somatosensory cortex (wS1). Each whisker is individually represented in the somatotopic map of wS1 by an anatomical unit named a ‘barrel’ (hence also called barrel cortex). This allows precise investigation of sensory processing in the context of a well-defined map. Here, we first review the signaling pathways from the whiskers to wS1, and then discuss current understanding of the various types of excitatory and inhibitory neurons present within wS1. Different classes of cells can be defined according to anatomical, electrophysiological and molecular features. The synaptic connectivity of neurons within local wS1 microcircuits, as well as their long-range interactions and the impact of neuromodulators, are beginning to be understood. Recent technological progress has allowed cell-type-specific connectivity to be related to cell-type-specific activity during whisker-related behaviors. An important goal for future research is to obtain a causal and mechanistic understanding of how selected aspects of tactile sensory information are processed by specific types of neurons in the synaptically connected neuronal networks of wS1 and signaled to downstream brain areas, thus contributing to sensory-guided decision-making.

Surface-based Map Plasticity of the Sensorimotor Cortex in Hip Disorder at Local and Extensive Levels: A Resting-state fMRI Study

Background: Pain is one of the manifestations of hip disorder and has been proven to lead to the remodeling of somatotopic map plasticity in the cortex. However, it’s not clear whether hip disorder with pain induces somatotopic map plasticity in the cortex. We aimed to evaluate the surface-based map plasticity of the somatotopic cortex in hip disorder at local and extensive levels by resting-state functional magnetic resonance imaging (rs-fMRI).Methods: 20 patients with osteonecrosis of the femoral head (ONFH) (12 males and 8 females, age= 56.80±13.60 years) with Visual Analogue Scale (VAS) scores ≥ 4 and 20 healthy controls (9 males and 11 females, age= 54.56±10.23 years) were enrolled in this study. rs-fMRI data and T1 imaging data were collected, and surface-based regional homogeneity (ReHo), seed-based functional connectivity (FC), cortical thickness and the volume of subcortical gray nuclei were calculated.Results: Compared with the healthy controls, the ONFH patients showed significantly increased surface-based ReHo in areas distributed mainly in the left dorsolateral prefrontal cortex and frontal eye field, the right frontal eye field and the premotor cortex and decreased surface-based ReHo in the right primary motor cortex and primary sensory cortex. When the area with decreased surface-based ReHo in the frontal eye field and right premotor cortex was used as the regions of interest (ROI), compared with the controls, the ONFH patients displayed increased FC in the right middle frontal cortex and right inferior parietal cortex and decreased FC in the right precentral cortex and right middle occipital cortex. ONFH patients also showed significantly decreased cortical thickness in the para-insular area, supplementary motor cortex area and frontal eye field and decreased volume of subcortical gray matter nuclei in the right nucleus accumbens (479.32±88.26 vs 539.44±68.36, P=0.026). Conclusions: Hip disorder patients showed cortical plasticity changes, mainly in sensorimotor and pain-related regions.

Prenatal activity from thalamic neurons governs the emergence of functional cortical maps in mice

The mammalian brain’s somatosensory cortex is a topographic map of the body’s sensory experience. In mice, cortical barrels reflect whisker input. We asked whether these cortical structures require sensory input to develop or are driven by intrinsic activity. Thalamocortical columns, connecting the thalamus to the cortex, emerge before sensory input and concur with calcium waves in the embryonic thalamus. We show that the columnar organization of the thalamocortical somatotopic map exists in the mouse embryo before sensory input, thus linking spontaneous embryonic thalamic activity to somatosensory map formation. Without thalamic calcium waves, cortical circuits become hyperexcitable, columnar and barrel organization does not emerge, and the somatosensory map lacks anatomical and functional structure. Thus, a self-organized protomap in the embryonic thalamus drives the functional assembly of murine thalamocortical sensory circuits.

Dorsal-to-ventral neocortical expansion is physically primed by ventral streaming of early embryonic preplate neurons

SummaryMammalian neocortex exhibits a disproportionally “luxurious” representation of somatotopies in its lateral region, which depends on dorsal-to-ventral expansion of the pallium during development. Despite recent studies elucidating the molecular mechanisms underlying the cortical arealization/patterning, we know very little about how the cortex expands ventrally and the nature of the underlying force-generating events. We found that neurons born earliest (at embryonic day 10 [E10]) in the mouse pallium migrated ventrally and then extended corticofugal axons, which together formed a morphogenetic flow of the preplate that persists until E13. These neurons exerted pulling and pushing forces at the process and the soma, respectively. Ablation of these E10-born neurons attenuated both deflection of radial glial fibers (by E13) and extension of the cortical plate (by E14), which should occur ventrally, and subsequently shrank the postnatal neocortical map dorsally. This previously unrecognized preplate stream physically primes neocortical expansion and somatotopic map formation.

Spinal cord injury below-level neuropathic pain relief with dorsal root entry zone microcoagulation performed caudal to level of complete spinal cord transection

OBJECTIVESurgically created lesions of the spinal cord dorsal root entry zone (DREZ) to relieve central pain after spinal cord injury (SCI) have historically been performed at and cephalad to, but not below, the level of SCI. This study was initiated to investigate the validity of 3 proposed concepts regarding the DREZ in SCI central pain: 1) The spinal cord DREZ caudal to the level of SCI can be a primary generator of SCI below-level central pain. 2) Neuronal transmission from a DREZ that generates SCI below-level central pain to brain pain centers can be primarily through sympathetic nervous system (SNS) pathways. 3) Perceived SCI below-level central pain follows a unique somatotopic map of DREZ pain-generators.METHODSThree unique patients with both intractable SCI below-level central pain and complete spinal cord transection at the level of SCI were identified. All 3 patients had previously undergone surgical intervention to their spinal cords—only cephalad to the level of spinal cord transection—with either DREZ microcoagulation or cyst shunting, in failed attempts to relieve their SCI below-level central pain. Subsequent to these surgeries, DREZ lesioning of the spinal cord solely caudal to the level of complete spinal cord transection was performed using electrical intramedullary guidance. The follow-up period ranged from 1 1/2 to 11 years.RESULTSAll 3 patients in this study had complete or near-complete relief of all below-level neuropathic pain. The analyzed electrical data confirmed and enhanced a previously proposed somatotopic map of SCI below-level DREZ pain generators.CONCLUSIONSThe results of this study support the following hypotheses. 1) The spinal cord DREZ caudal to the level of SCI can be a primary generator of SCI below-level central pain. 2) Neuronal transmission from a DREZ that generates SCI below-level central pain to brain pain centers can be primarily through SNS pathways. 3) Perceived SCI below-level central pain follows a unique somatotopic map of DREZ pain generators.