Biology subjects

Semework, M.

Publications and source records attributed to Semework, M..

5 recordsLinked to original sources

bioRxiv2021

Similarities Between Somatosensory Cortical Responses Induced via Natural Touch and Microstimulation in the Ventral Posterior Lateral Thalamus in Macaques

Lost sensations, such as touch, could be restored by microstimulation (MiSt) along the sensory neural substrate. Such neuroprosthetic sensory information can be used as feedback from an invasive brain-machine interface (BMI) to control a robotic arm/hand, such that tactile and proprioceptive feedback from the sensorized robotic arm/hand is directly given to the BMI user. Microstimulation in the human somatosensory thalamus (Vc) has been shown to produce somatosensory perceptions. However, until recently, systematic methods for using thalamic stimulation to evoke naturalistic touch perceptions were lacking. We have recently presented rigorous methods for determining a mapping between ventral posterior lateral thalamus (VPL) MiSt, and neural responses in the somatosensory cortex (S1), in a rodent model (Choi et al., 2016; Choi and Francis, 2018). Our technique minimizes the difference between S1 neural responses induced by natural sensory stimuli and those generated via VPL MiSt. Our goal is to develop systems that know what MiSt will produce a given neural response and possibly a more natural "sensation." To date, our optimization has been conducted in the rodent model and simulations. Here we present data from simple non-optimized thalamic MiSt during peri-operative experiments, where we MiSt in the VPL of macaques with a somatosensory system more like humans. We implanted arrays of microelectrodes across the hand area of the macaque S1 cortex as well as in the VPL thalamus. Multi and single-unit recordings were used to compare cortical responses to natural touch and thalamic MiSt in the anesthetized state. Post stimulus time histograms were highly correlated between the VPL MiSt and natural touch modalities, adding support to the use of VPL MiSt towards producing a somatosensory neuroprosthesis in humans.

neuroscience↗

bioRxiv2019

Distinct signatures of reward value and variance on spiking activity and functional interactions in monkey fronto-parietal areas

Theories of executive function propose that controlled information processing is costly and is allocated according to the behavioral benefits it brings. Computational theories predict that the benefits of new information depend on prior uncertainty, but the cellular effects of uncertainty on the executive network are incompletely understood. Using simultaneous recordings in monkeys, we reveal several mechanisms by which the fronto-parietal network reacts to uncertainty independently of average reward gains. We show that the variance of expected rewards, independently of the value of the rewards, was represented in single neuron and population spiking activity and local field potential (LFP) oscillations. Moreover, uncertainty asymmetrically affected the coherence between spikes and LFPs, selectively suppressing information transmission from the frontal to the parietal lobe but enhancing transmission from the parietal to the frontal lobe, consistent with Bayesian principles of optimal inference under uncertainty.

neuroscience↗

bioRxiv2019

Frontal and parietal neurons encode reward prediction errors in multiple reference frames

Computing expectancy violations is essential for decision making and cognitive functions, but its neural mechanisms are incompletely understood. We describe a novel mechanism by which prefrontal and posterior parietal neurons encode reward prediction errors (RPEs) in their population but not single-neuron activity. Simultaneous recordings of neural populations showed that both areas co-activated information about experienced and expected rewards in a precise opponent organization. Neurons encoding expected rewards with positive (negative) scaling were reactivated simultaneously with those encoding experienced rewards with negative (positive) scaling. This opponent organization was mirrored in polarity-dependent noise correlations. Moreover, it extended to two types of expectancy information - based on task-relevant visual cues and statistically irrelevant reward history - allowing decoding of signed and unsigned RPE in two reference frames. Frontal and parietal areas implement canonical computations that facilitate contextual comparisons and the readout of multiple types of expectancy violations to flexibly serve behavioral goals.

neuroscience↗

bioRxiv2018

Electrophysiological evidence for cerebellar involvement in higher-order cognitive processing

Although the cerebellum has been traditionally considered to be exclusively involved in motor control and learning, recent anatomical and clinical studies suggest that it may also have a role in cognition. However, no electrophysiological evidence exists to support this claim. Here we studied the activity of simple spikes of hand-movement related Purkinje cells in the mid-lateral cerebellum when monkeys learned to associate a well-learned right or left-hand movement with one of two visual symbolic cues. The cells had distinctly different discharge patterns between an overtrained symbol-hand association and a novel symbol-hand association although the kinematics of the movement did not change between the two conditions. The activity change was not related to the pattern of the visual symbols, the hand making the movement, the monkeys reaction times or the novelty of the visual symbols. We suggest that mid-lateral cerebellum is involved in higher-order cognitive processing related to learning a new visuomotor association.\n\nOne Sentence SummaryHand-movement related Purkinje neurons in midlateral cerebellum, which discharge during an overtrained visuomotor association task, change their activity when the monkey has to associate the same movements with new cues, even though the kinematics of the movements do not change.

neuroscience↗

bioRxiv2017

A spatial memory signal shows that the parietal cortex has access to a craniotopic representation of space

Humans effortlessly establish a gist-like memory of their environment whenever they enter a new place. They can then use this memory to guide action even in the absence of vision. Neurons in the lateral intraparietal area (LIP) of the monkey exhibit a form of this environmental memory, responding when a monkey makes a saccade that brings the spatial location of a stimulus that appeared on a number of prior trials, but not on the present trial into their receptive fields. The stimulus need never have appeared in the receptive field of the neuron. This response is usually weaker with a longer latency than the neuron's visual response. We suggest that these results demonstrate that LIP has access to a craniotopic memory of space, which is activated when the spatial location of the vanished stimulus can be described by a retinotopic vector from the center of gaze to the stimulus.

neuroscience↗