Visual evoked potentials in Duchenne muscular dystrophy
Benoff, Keith Richard
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Visual evoked potential (VEP) research is a means of acquiring a better understanding of the neural processing of visually-presented information. The VEP is a noninvasive electrophysiological measurement to visual stimulation. The response is the individual's neuronal activity in the form of small electrical currents giving rise to electrical potentials measured off the scalp.;Transmission of vision information in individuals with Duchenne muscular dystrophy (DMD) has been evaluated with electroretinograms (ERGs), including Cibis, Fitzgerald, Harris, Rothberg, & Rupani (1993); DeBecker, Dooley, & Tremblay (1993) & Fitzgerald, Cibis, Giambrone, & Harris, 1994; Pillers, Weleber, Green, Rash, Dally, Howard, Powers, Hood, Chapman, Ray, & Woodward (1999). Whereas the electroretinogram measures the response at the retinal level, the VEP extends beyond, into cortical regions.;ERGs of individuals with DMD with a deletion on the dystrophin gene downstream of exon 44 from the ERG of individuals with no neurologic disorder. These studies demonstrate an ON pathway deficit, as the prominent b-wave is missing. The goal of this study was to ascertain whether their VEPs as well, and if the difference resembles that of the ERG difference.;Eight children with DMD were compared to eight age-matched children with no neurologic disorder. A bright isolated-check luminance contrast condition (driving the ON pathway) elicited lower amplitudes and signal-to-noise ratios for the DMD group, but the shape of the function was similar for both groups. A bright isolated check-size sweep evidenced lower amplitude at low and moderate spatial frequencies. A dark isolated-check luminance contrast condition (driving the OFF pathway) did not elicit any differences between the two groups, while the dark isolated check-size sweep elicited differences only at two lower spatial frequencies. Differences for both check-size sweeps at lower spatial frequencies reflects cortical inhibition, whereas the differences for the bright contrast condition and moderate spatial frequencies of the bright check-size sweep reflects a lack of input from the Magnocellular-ON pathway. Conventional and swept-parameter transient conditions revealed significantly lower magnitude-squared coherence estimates for the DMD group then the age-matched control group for the middle frequency harmonics, and smaller differences for the lower harmonic frequencies.
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