Biology subjects

Goodman, J. M.

Publications and source records attributed to Goodman, J. M..

5 recordsLinked to original sources

bioRxiv2024

Changes in cortical grasp-related activity before and after object contact

The transition from hand opening to grasping a coffee cup happens smoothly, yet the neural systems underlying this behavior undergo a significant state change at the onset of grasp. At this moment, the motor system begins to control contact forces and the somatosensory system receives a barrage of cutaneous signals that convey information about contact forces and the objects local features (e.g., edges, texture, and curvature). These cutaneous signals supplement the ongoing flow of proprioceptive input that encodes hand posture as well as muscle forces. How object identity is represented in sensorimotor cortex across this transition remains unknown. In the present study, we sought to quantify the object-specific neural signals in individual neurons of the primary motor cortex (M1) and Brodmann areas 3a, 3b/1, and 2 of the somatosensory cortex in macaque monkeys. Before contact, object-specific information was carried mainly by M1 and proprioceptive area 3a, but this information did not generalize between the periods before and after contact. This observation is consistent with the abruptly changing force signals at contact affecting the assumed postural representation of the object, rather than each modality maintaining an invariant identity. After contact, despite a general decrease in firing rates, information about object identity increased and was encoded with high efficiency across sensorimotor cortex. Cutaneous areas 3b and 1, largely uninformative before contact, became highly informative once objects were grasped. Area 2, which receives both cutaneous and musculotendinous inputs, conveyed little object-specific information before contact, when it too became strongly informative, consistent with its integrative role. Thus, M1 and 3a serve as the main carriers of object information before contact, while cutaneous and integrative somatosensory circuits dominate after contact. This shift highlights the profound change in the coding of object identify in the sensorimotor cortex during contact.

neuroscience↗

bioRxiv2021

Seipin forms a flexible cage at lipid droplet formation sites

Lipid droplets (LDs) form in the endoplasmic reticulum by phase separation of neutral lipids. This process is facilitated by the seipin protein complex, which consists of a ring of seipin monomers, with yet unclear function. Here, we report a structure of yeast seipin based on cryo-electron microscopy and structural modeling data. Seipin forms a decameric, cage-like structure with the lumenal domains forming a stable ring at the cage floor and transmembrane segments forming the cage sides and top. The transmembrane segments interact with adjacent monomers in two distinct, alternating conformations. These conformations result from changes in switch regions, located between the lumenal domains and the transmembrane segments, that are required for seipin function. Our data suggest a model for LD formation in which a closed seipin cage enables TG phase separation and subsequently switches to an open conformation to allow LD growth and budding.

molecular biology↗

bioRxiv2019

Unexpected Complexity Of Everyday Manual Behaviors

AO_SCPLOWBSTRACTC_SCPLOWHow does the brain control an effector as complex and versatile as the hand? One possibility is that the neural control of the hand is simplified by limiting the space of achievable hand postures. Indeed, hand kinematics can be largely accounted for within a small subspace of postures. This oft replicated finding has been interpreted as evidence that hand postures are confined to this subspace, and that leaving it volitionally is impossible. A prediction from this hypothesis is that measured hand movements that fall outside of this subspace reflect motor or measurement noise. To address this question, we track hand postures of human participants as they perform two distinct tasks - grasping and signing in American Sign Language. We then apply a standard dimensionality reduction technique - principal components analysis - and replicate the finding that hand movements can be largely described within a reduced subspace. However, we show that postural dimensions that fall outside of this subspace are highly structured and task dependent, suggesting that they too are under volitional control. We conclude that hand control occupies a higher dimensional space than previously considered, and propose that controlling the complexity of hand movements is well within the scope of the brains computational power.

neuroscience↗

bioRxiv2019

NEURAL POPULATION DYNAMICS IN MOTOR CORTEX ARE DIFFERENT FOR REACH AND GRASP

AO_SCPLOWBSTRACTC_SCPLOWRotational dynamics are observed in neuronal population activity in primary motor cortex (M1) when monkeys make reaching movements. This population-level behavior is consistent with a role for M1 as an autonomous pattern generator that drives muscles to produce movement. Here, we show that M1 does not exhibit smooth dynamics during grasping movements, suggesting a more input-driven circuit.

neuroscience↗

bioRxiv2019

Postural representations of the hand in primate sensorimotor cortex

Dexterous hand control requires not only a sophisticated motor system but also a sensory system to provide tactile and proprioceptive feedback. To date, the study of the neural basis of proprioception in cortex has focused primarily on reaching movements, at the expense of hand-specific behaviors such as grasp. To fill this gap, we record both the time-varying hand kinematics and the neural activity evoked in somatosensory and motor cortices as monkeys grasp a variety of different objects. We find that neurons in somatosensory cortex, as well as in motor cortex, preferentially track postures of multi-joint combinations spanning the entire hand. This contrasts with neural responses during reaching movements, which preferentially track movement kinematics of the arm rather than its postural configuration. These results suggest different representations of arm and hand movements likely adapted to suit the different functional roles of these two effectors.

neuroscience↗