30th Annual Meeting Program

Abstract to come

Chairs: Dagmar Sternad¹ & Andrea d’Avella⁵

Presenters: Dagmar Sternad¹, Marta Russo¹, Antonella Maselli², Christian Rutz³, Aude Billard⁴, Andrea d’Avella⁵

Confirmed Discussants: Dagmar Sternad and Andrea d’Avella

¹Northeastern University, Policlinico Tor Vergata, ²Consiglio Nazionale delle Ricerche, ³University of St. Andrews, ⁴Swiss Federal Institute of Technology in Lausanne (EPFL), ⁵University of Messina

Functional interaction with objects – tool use – is essential in daily living and is regarded as the foundation for our evolutionary advantage. Surprisingly, however, how humans control objects or tools is still little understood. Manipulation of objects presents considerable additional control challenges beyond those in unconstrained reaching and pointing. This is readily highlighted in robotics where contact instability still presents a significant hurdle for robot manipulation and robot-human collaboration. Beyond interaction, the control of complex objects invariably requires more than a simplified end effector, two hands and the whole body, bringing the issue of redundancy front and center. This panel will focus on complex actions and interactions with complex objects that are still largely unchartered territory in motor neuroscience to date. Two speakers will feature novel methodological approaches on complex manual skills in humans; one speaker will present the challenges from the perspective of synthesis, i.e., the generation of dexterous robot manipulation; one speaker will showcase the unusually sophisticated tool behavior in New Caledonian crows that proved wrong the widely-held assumption that tool use is unique to humans. Together, the panel will raise questions on neural, mechanical, and genetic contributions necessary to achieve such intricate coordinate feats. Marta Russo will present recent work on whip manipulation. Using full-body motion capture, the study examined participants of different skill levels. She will show a three-pronged strategy to identify control principles in this prodigiously complex action: Analysis of the complex arm dynamics, analysis of the whip dynamics, and synthesis in simulation engines testing control elements or primitives. Antonella Maselli will present work on throwing of a ball to a target. She will show how spatiotemporal principal component decomposition of whole-body kinematics provides a compact way to identify individual strategies. Four main throwing styles are extracted that resemble different stages of throwing skill acquisition reported in motor development studies. Christian Rutz will introduce a non-primate model system for studying tool behaviors. New Caledonian crows exhibit striking dexterity when manufacturing tools from plant materials, when using these tools to extract insect prey from deadwood, and when storing tools in small holes. Remarkably, they achieve this dexterity with only simple ‘two-pronged grippers’, their bills. Aude Billard will provide a robotics perspective to tool manipulation. To understand and model this dexterity, her team examined cohorts of apprentices at watchmaking, a craft unique in the precision of control it requires. Her work unveils how two hands work in coordination to distribute control variables and achieve better precision than a single hand. Early work in transferring some of this ability to robotic hands will also be presented.

Chair: Eiman Azim¹

Presenters: Eiman Azim¹, Sliman Bensmaia², Corinna Darian-Smith³, Kazuhiko Seki⁴

Confirmed Discussant: Chris Versteeg⁵

¹ Salk Institute for Biological Studies, ²University of Chicago, ³Stanford University School of Medicine, ⁴National Institute of Neuroscience, National Center of Neurology and Psychiatry, ⁵Feinberg School of Medicine, Northwestern University

A critical challenge faced by the mammalian motor system is the coordination of dozens of muscles in the forelimbs to interact with the world. The precision of forelimb behaviors implies feedback pathways dedicated to the ongoing refinement of motor output. The dorsal column nuclei (DCN), located in the brainstem, represent the major conduit of somatosensory information from the periphery to supraspinal targets. Of the DCN, the cuneate nuclei are tasked with receiving and processing forelimb cutaneous and proprioceptive signals and conveying the resulting sensory information to the sensorimotor cortex via cuneolemniscal projections to the thalamus (amongst other subcortical targets). The cuneate nuclei also receive a diversity of other inputs, including from the cerebral cortex, suggesting top-down modulation of sensory signals. Defining how the nervous system orchestrates behavior demands an understanding of how feedback represents and refines movements, and the cuneate nuclei provide a fundamental and tractable location for exploring the anatomical and functional logic of feedback control. By describing recent progress in our understanding of the cuneate in primates and mice, this panel aims to integrate diverse approaches into a more complete description of sensorimotor control. Four speakers were selected for their ongoing work exploring how cuneate neurons process different types of sensory information, how these signals are modulated by descending pathways during behavior, and how cuneate circuits respond to injury and are rewired to restore function. Kazuhiko Seki will present anatomical, electrophysiological, and behavioral findings that delineate bottom-up and top-down inputs to the cuneate nucleus of nonhuman primates, providing insight into how cutaneous and proprioceptive feedback might be modulated during movement. Sliman Bensmaia will describe how tactile responses in primate cuneate imply the convergence and processing of signals from multiple cutaneous submodalities, which are then subject to top-down influences. Eiman Azim, will discuss work in mice identifying local and descending circuits that modify cutaneous feedback in the cuneate and participate in the execution of tactile-guided behaviors. Corinna Darian-Smith will describe how cuneate circuits respond to injury of sensory pathways, and how compensatory rewiring can aid functional recovery. Chris Versteeg will then lead a panel discussion focused on key themes, including: a) How movement affects the transmission of sensory feedback and the implications of this modulation for refining motor output; b) How somatosensory processing in the cuneate might relate to other sensory modalities; c) The degree to which different aspects of feedback circuit organization are conserved across mammalian species, and what this might teach us about human sensorimotor control.

In order to link perception and action the brain must have a spatially accurate representation of the visual world, so it can generate actions appropriate to the objects it perceives. The only way visual information enters the eye is through the retina, which moves constantly between brief fixations. The retinal location of targets for action is not useful for calculating movements to acquire those targets. Two strategies have been postulated to calculate the accurate location of movement targets: Helmholtz suggested that the brain knows the command to move the eye, and therefore can use that motor command to update the sensory representation. This feedback from the motor system to the sensory system is now known as corollary discharge. Sherrington suggested that the brain can calculate accurate target location if it knows the position of the eye in the world, and the first step in this process is to know the position of the eye in the orbit. He postulated that this signal arose from oculomotor proprioceptors. The lateral intraparietal area (LIP) is a brain region important in choosing targets for saccadic eye movements, and solves the spatial accuracy problem using both Helmholtz’s and Sherrington’s strategies: a rapid, relatively accurate corollary discharge mechanism, and a slower, but more accurate proprioceptive mechanism, which is dependent upon the sensory representation of eye position in Area 3a of the primary somatosensory cortex.