Biology subjects

Ghulam-Jelani, Z.

Publications and source records attributed to Ghulam-Jelani, Z..

3 recordsLinked to original sources

bioRxiv2026

Flexible reorientation of conserved neural dynamics underlies grasp control

Grasping objects is a complex behavior requiring high-dimensional hand control and dynamic interaction with the environment, yet its neural mechanisms remain poorly understood. Dynamical systems approaches have provided key insights into how neural populations generate control signals for arm movements such as reaching and cycling but have proven insufficient to account for neural population activity during grasping. Here, we re-analyzed multi-area neural recordings from rhesus monkeys performing a reach-to-grasp task to many objects and found two key population-level features. First, the component of the population trajectory that was common to all grasps formed a small angle with the subspace containing grasp condition-specific (object) tuning. Second, the neural activity was well fitted by a recent, flexible dynamical model developed for reaching, called location-dependent rotations (LDR). Neural activity in M1 and F5 during grasping exhibited conserved population-level rotational frequencies, but the state-space planes in which these rotations occurred varied systematically with grasp condition. The rotational center (the location) and the orientation of the rotations related both to each other and to the kinematics of movement. While these rotations were reoriented in high dimensional space, reflecting the high-dimensional nature of hand control, the extent of their tilt into additional dimensions were small, in contrast to reaching. This structure may reflect the nature of grasping as modulations of an overall open-close motif. Together, these results indicate that the LDR dynamics framework applies to grasping as well as reaching and provides an entry point to understanding how grasp commands are generated.

neuroscience↗

bioRxiv2020

Redundancy Circuits of the Commissural Pathways in Human and Rhesus Macaque Brains

It has been hypothesized that the human brain has traded redundancy for efficiency, but the structural existence has not been identified to examine this claim. Here, we report three redundancy circuits of the commissural pathways in primate brains, namely the orbitofrontal, temporal, and occipital redundancy circuits of the anterior commissure and corpus callosum. Each redundancy circuit has two distinctly separated routes connecting a common pair of cortical regions. We mapped their trajectories in human and rhesus macaque brains using individual and population-averaged tractography. The dissection results confirmed the existence of these redundancy circuits connecting the orbitofrontal lobe, amygdala, and visual cortex. The volume analysis showed a significant reduction in the orbitofrontal and occipital redundancy circuits of the human brain, whereas the temporal redundancy circuit had a substantial organizational difference between the human and rhesus macaque. Our overall findings suggest that the human brain is more efficient in the commissural pathway, as shown by the significantly reduced volume of the anterior commissure which serves as the backup connections for the corpus callosum. This reduction of the redundancy circuit may explain why humans are more vulnerable to psychiatric brain disorders stemming from the corpus callosum compared to non-human primates. SignificanceWe report and describe the connection routes of three redundancy circuits of the commissural pathways in human and rhesus macaque brains and compare their volumes. Our tractography and dissection studies confirmed that the human brain has smaller redundancy circuits. This is the first time such redundancy circuits of the commissural pathways have been identified, and their differences quantified in human and rhesus macaque to verify the redundancy-efficiency tradeoff hypothesis. The findings provide new insight into the topological organization of the human brain and may help understand the circuit mechanism of brain disorders involving these pathways.

neuroscience↗

bioRxiv2019

Gram-positive and Gram-negative Bacteria Share Common Principles to Coordinate Growth and the Cell Cycle at the Single-cell Level

Bacillus subtilis and Escherichia coli are evolutionarily divergent model organisms that have elucidated fundamental differences between Gram-positive and Gram-negative bacteria, respectively. Despite their differences in cell cycle control at the molecular level, both organisms follow the same phenomenological principle for cell size homeostasis known as the adder. We thus asked to what extent B. subtilis and E. coli share common physiological principles in coordinating growth and the cell cycle. To answer this question, we measured physiological parameters of B. subtilis under various steady-state growth conditions with and without translation inhibition at both population and single-cell level. These experiments revealed core shared physiological principles between B. subtilis and E. coli. Specifically, we show that both organisms maintain an invariant cell size per replication origin at initiation, with and without growth inhibition, and even during nutrient shifts at the single-cell level. Furthermore, both organisms also inherit the same \"hierarchy\" of physiological parameters ranked by their coefficient of variation. Based on these findings, we suggest that the basic coordination principles between growth and the cell cycle in bacteria may have been established in the very early stages of evolution.

systems biology↗