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

Abstract

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.