The Effect of Experimental Concussion on Somatosensory Evoked Potentials

Abstract

Summary, Cortical somatosensory evoked potentials (SEPs) were recorded following experimental acceleralion concussion in the rat. Immediately after head injury there was a general reduction in Ihe amplitude of Ihe SEP, and all ils components were either temporarily abolished or increased in latency. The early components of the SEP recovered much more rapidly than did the amplitude and latencies of the later potentials. The purpose of the study was to investigate the relative cITccts of concussion on the lemniscal system (whose activity is reflected by the discrete early components of the SEP) and the reticular activating system (whose activity is reflected hy the ditfuse high amplitude late component of the SEP). Conlrary to a widely accepted theory, there was a delay in transmission of somatosensory information through the lemniscal pathways as well as through the reticular system following head injury. Such an observation is consistenl with recent studies of SEPs recorded from humans comatose after head trauma. As the changes in the morphology of the waveform of the SEP following concussion can be simulated by simply recording evoked potentials at high rales of stimulation, this suggests that the delays are caused by a failure or malfunction of .synaptic transmission, but the level at which this i.s occurring remains to be determined.

Disconnection and hyper-connectivity underlie reorganization after TBI: A rodent functional connectomic analysis

“…While there are significant decreases in blood flow (Richards et al, 1995; Chen et al, 2004) and electrophysiologic activity (Shaw and Cant, 1984) acutely after CCI injury, blood-flow elicited response to forelimb stimulation suggest that coupling may be intact by 4 days post-injury (Harris et al, 2013a,b), preventing any confound in the data at 7 days. Regardless, the majority of the connectivity changes were not solely focused on the ipsilateral cortex, the region most likely to be affected by uncoupling so that any confound due to uncoupling is likely to be minimized at the post-injury times studied in this work.…”

Multiple Spectral Inputs Improve Motion Discrimination in the Drosophila Visual System

“…3H and fig. S5C), implying that they receive information from R7/R8s (28, 29) through functional contacts, as in UV flies (Fig. 2C and fig.…”

“…Although motion information appears routed and processed through dedicated on and off channels (11, 26, 27), in principle R1–R6 channels might cross-talk with the color channels in places. Ultrastructural studies imply interactions in the medulla, with synapses between R7/R8 photo-receptors and LMCs (24), but possibly also in the lamina, where gap junctions (28, 29) and synapses (13) form sophisticated local processing networks (30). Here, combining information from different channels could improve the sensitivity, precision, and robustness of their neural messages.…”

“…2E) in which one photoreceptor (R6 or neighboring R1) receives information from either a R8y or R8p cell, in keeping with results from larger dipteran flies (fig. S7) (28, 29). This input would then spread decrementally between R1–R6 via gap junctions (29, 36), showing diminishing green-yellow sensitivity the farther a recorded photoreceptor is from a R6 in the cartridge (fig.…”

“…However, transfer of long-wavelength (595 nm) information in presumptive R6s (Fig. 3, D and E)—that is, ~12% of R1–R6 photoreceptors, which receive the direct feed from R8y photoreceptors (28, 29) of the color pathway [70% lamina cartridges (16)]—could be as high as 70% compared with that of a similar UV stimulus in the same cells (Fig. 3F), indicating efficient communication between R8 and R6 axons.…”