Biology subjects

Parikh, P. J.

Publications and source records attributed to Parikh, P. J..

2 recordsLinked to original sources

bioRxiv2019

Intertrial Variability in Human Corticospinal Activity during Grasp Force Planning

Neuronal firing rate variability during planning has been found to contribute to trial-to-trial variability in primate behavior. However, in humans, whether planning related mechanisms contribute to trial-to-trial behavioral variability remains unknown. We investigated the time-course of trial-to-trial variability in corticospinal excitability (CSE) using transcranial magnetic stimulation (TMS) while subjects planned to perform a self-paced reach-to-grasp task. We hypothesized that CSE variability will be modulated during task planning and that such a modulation would explain trial-to-trial behavioral variability. Able-bodied individuals were visually cued to plan their grip force before exertion of either 30% or 5% of maximum force on an object. TMS was delivered at different time points following a cue that instructed the force level. We first modeled the relation between CSE magnitude and its variability at rest (n=12) to study the component of CSE variability during task planning that was not related to changes in CSE magnitude (n=12). We found an increase in CSE variability during task planning at 30% but not at 5% of force. This effect was temporally dissociated from the decrease in CSE magnitude. Importantly, the increase in CSE variability during planning explained 64% of inter-individual differences in time to peak force rate trial-to-trial variability. These results were found to be repeatable across studies and robust to different analysis methods. Our findings suggest that the planning-related mechanisms underlying modulation in CSE variability and CSE magnitude are distinct. Notably, the extent of modulation in planning-related variability in corticospinal system within individuals may explain their trial-to-trial behavioral variability.

neuroscience↗

bioRxiv2019

Choice of Contact Points Modulates Sensorimotor Cortical Interactions for Dexterous Manipulation

Humans are unique in their ability to perform dexterous object manipulation in a wide variety of scenarios. However, previous work has used a grasping context that predominantly elicits memory-based control of digit forces by constraining where the object should be grasped. For this constrained grasping context, primary motor cortex (M1) is involved in storage and retrieval of digit forces used in previous manipulations. In contrast, when choice of digit contact points is allowed ( unconstrained grasping), behavioral studies revealed that forces are adjusted, on a trial-to-trial basis, as a function of digit position. This suggests a role of online feedback that detects digit position, rather than memory, for force control. However, despite the ubiquitous nature of unconstrained hand-object interactions in activities of daily living, the underlying neural mechanisms are unknown. Using non-invasive brain stimulation and electroencephalography, we found the role of M1 to be sensitive to grasping condition. While confirming the role of M1 in storing and retrieving learned digit forces and position in constrained grasping, we also found that M1 is involved in modulating digit forces to digit position in unconstrained grasping. Furthermore, we found that digit force modulation to position relies on sensorimotor integration mediated by primary sensory cortex (S1) and M1. This finding supports the notion of a greater contribution of somatosensory feedback of digit position in unconstrained grasping. We conclude that the relative contribution of memory and online feedback based on whether contact points are constrained or unconstrained modulates sensorimotor cortical interactions for dexterous manipulation.

neuroscience↗