Biology subjects

Barbay, S.

Publications and source records attributed to Barbay, S..

4 recordsLinked to original sources

bioRxiv2020

Functional Suppression of Premotor Activity in a Transient Model of Motor Cortex Injury

Cortical injuries (e.g. - strokes or traumatic brain injuries) can create a host of secondary events that further impair the brains sensory, motor, or cognitive capabilities. Here, we attempted to isolate the acute effects of the primary injury - the loss of cortical activity - on rodent motor cortex (caudal forelimb area, CFA) without the secondary effects that arise from damage to cortical tissue. We then observed the effects of this loss of activity on the rodent premotor cortex (rostral forelimb area, RFA). In anesthetized rats, CFA was temporarily inactivated with the GABA-A agonist muscimol, disrupting motor network function while leaving neural connectivity intact. Using intracortical microstimulation (ICMS) techniques, we found that CFA inactivation completely abolished ICMS-evoked forelimb movement from RFA yet spared some CFA evoked-movement. Neural recordings confirmed that neural suppression by muscimol was isolated to CFA and did not spread into RFA. We next observed how CFA inactivation suppressed RFA influence on forelimb muscles by obtaining intramuscular electromyographical (EMG) recordings from forelimb muscles during ICMS. EMG recordings showed that despite the presence of evoked movement in CFA, but not RFA, muscle activation in both areas were similarly reduced. These results suggest that the primary reason for the loss of ICMS-evoked movement in RFA is not reduced forelimb muscle activity, but rather a loss of the specific activity between RFA and CFA. Therefore, within the intact motor network of the rat, RFAs influence on forelimb movement is mediated by CFA, similar to the premotor and motor organization observed in non-human primates.

neuroscience↗

bioRxiv2020

Anatomical Plasticity of the Distal Forelimb Projection of the Ventral Premotor Cortex Four weeks After Primary Motor Cortex Injury

Brain injury affecting the isocortical frontal cortex is a common pathological occurrence. Many patients report severe deficits to functions of daily living. However, there is a variable degree of motor recovery that occurs with some individuals recovering astounding degrees of motor recovery while others have not. This variability has led researchers into investigating the possible mechanisms for this variability. Recently, several non-human primate studies have shed light on the possibility of spared, ipsilesional motor area taken over the lost function to the damaged cortex. Unfortunately, these studies have focused on long-term adaption ranging from 5months to one year post injury. In this present study, we are the first use rigorous stereological quantification to show that significant neuroplastic changes in the form of changes to neuroanatomical connections between distant cortical area occurs at a very early time point of 4 weeks post injury. Much like the Dancause study in 2005, we found that ishemic damage to the distal forelimb area (DFL) of the primary motor cortex (M1) induced plastic changes between the DFL of the ventral premotor cortex (PMv) and area 1/2 of the somatosensory cortex. Indeed, we found a nearly 2 fold increase in the number of boutons between PMV and area 1/2. Additionally, labeled fibers from PMv change direction from their normal termination within M1 and traveled in a ventral posterior direction toward the somatosensory cortex. Also of interest, several labeled fibers actually traveled through the glial scar of M1 toward the somatosensory cortex. These data demonstrate that a massive neuroplastic response has occurred following an ischemic insult to the DFL of M1. These data may suggest that the brain may be undergoing an attempt to re-establish a degree of motor and or sensory control to compensate for the lost function due to the injury.

neuroscience↗

bioRxiv2020

Task Related Neural Activity Following Primary Motor Cortical Ischemic Injury in Rats

Acquired injuries to primary motor cortex (M1) contribute to motor impairment and disability. Functional recovery is predicated on the reorganization of spared areas, which has been demonstrated through cortical motor map representations and neuroanatomical projection and termination patterns. The purpose of this study was to understand how neurophysiological outputs of spared motor areas relate to motor recovery of a skilled reach task following an ischemic infarct to M1. We examined changes in single unit activity within ipsilesional pre-motor (PM) and contralesional M1 cortices of rats during a behavioral task after a unilateral ischemic injury to ipsilesional M1. The data show a shift in neuronal firing patterns in the contralateral PM and ipsilateral M1 during behavioral recovery in lesion rats compared to a non-lesion control group, suggesting that spike-timing properties are altered in specific phases of the task, and that this altered activity may support spontaneous restoration of motor behavior. SIGNIFICANCE STATEMENTFollowing ischemic stroke to primary motor cortex (M1), motor recovery is associated with reorganization of spared cortical motor areas in injured and spared hemispheres. Currently, it is unclear how cortical plasticity within spared motor areas relates to motor recovery. This study examines how task-related neural activity within spared motor areas in rats correlates with motor restoration of a skilled reach task following an ischemic infarct to M1. The data suggest contralateral pre-motor and ipsilateral M1 alter their neural response profiles with respect to the timing of a motor task during recovery. To our knowledge, this is the first demonstration of a compensatory single-spike neurophysiological mechanism that may explain how remote, spared cortical areas contribute to functional recovery after M1 injury.

neuroscience↗

bioRxiv2020

Corticocortical Connections of the Rostral Forelimb Area in Rats: A Quantitative Tract-Tracing Study

The rostral forelimb area (RFA) in the rat is considered to be a premotor cortical region based primarily on its efferent projections to the primary motor cortex. The purpose of the present study was to identify corticocortical connections of RFA, and to describe the relative strength of connections with other cortical areas. This will allow us to better understand the broader cortical network in which RFA participates, and thus, determine its function in motor behavior. In the present study, the RFA of adult male Long-Evans rats (n=6) was identified using intracortical microstimulation techniques and injected with the tract tracer, biotinylated dextran amine (BDA). In post-mortem tissue, location of BDA-labeled terminal boutons and neuronal somata were plotted and superimposed on cortical field boundaries. The results demonstrated that the RFA has dense to moderate reciprocal connections with primary motor cortex, the frontal cortex medial and lateral to RFA, primary somatosensory cortex (S1), and lateral somatosensory areas. Importantly, S1 connections were dense to moderate in dysgranular zones, but sparse to negligible in granular zones. Cortical connections of RFA in rat are strikingly similar to cortical connections of the ventral premotor cortex in non-human primates, suggesting that these areas share similar functions.

neuroscience↗