Somatosensory and visual evoked potentials in human aging
Kazis, A.; Vlaikidis, N.; Pappa, P.; Papanastasiou, J.; Vlahveis, G.; Routsonis, K.
Electromyography and Clinical Neurophysiology 23(1-2): 49-59
1983
ISSN/ISBN: 0301-150X PMID: 6840038 Document Number: 205368
In 23 normal aged individuals, 70-91 yr old (mean = 78.5 yr), and 21 controls, 21-40 yr old (mean = 30.5 yr), the latency and amplitude of the most basic early SEP N13, N20 and P114 were comparatively studied. With regard to aged individuals, the most important finding can be summarized as follows: decrease in sensory conduction velocity along the peripheral somatosensory pathway, normal sensory conduction velocity along the central somatosensory pathway, conduction velocity decrease in the visual pathway, decrease in the amplitude of component N13 of the spinal SEP, increase in amplitude of component N20 of the cortical SEP and P114 of the VEP and absence of significant differences between right and left recordings of SEP and VEP. Decrease in the conduction velocity of the peripheral somatosensory pathway is explained by the greater length of the 1st sensory neuron, which is more sensitive to the metabolic disturbances caused by aging than the more central sensory neurons, which are more resistant because of their smaller length. The delay in the transmission of the stimulus in the visual pathway is possibly due to disturbances in its peripheral section (lens, retina, etc). The greatest amplitude of the SEP and VEP which represents activation of the bioelectrical activity of the cortex and coincides with the greatest amplitude of the .alpha. rhythm in aged individuals is, according to 1 view, due to the decrease in the endocortical inhibitory mechanisms (GABA) and the resulting prevalence of the excitatory mechanisms. According to another view it is due to the development of dendritic branches in the cortical neurons which compensate for the degeneration of the synaptic spines. Without finding a difference between the left and right recordings in aged individuals, an asymmetry in the morphology and specifically in the amplitude (smaller) and duration (greater) of the components on the side with the slow waves was observed in individuals whose EEG showed slow temporal activity.