114. Physiological aging is associated with reorganization of map motor cortical representation and interhemispheric interactions: A TMS mapping study

Several functional studies suggest a more bilateral movement-related recruitment of motor areas during voluntary movement associated with physiological aging. To investigate the changes of motor cortical excitatory and inhibitory balance during physiological aging, using transcranial magnetic stimulation (TMS). We recruited right-handed 31 healthy volunteers, divided into two groups: one younger group (15 subjects, 6 females, age 25.4 ± 1.9 y) and one older group (16 subjects, 7 females, age 61.1 ± 5.1 y). Motor abilities were tested using Nine Hole Peg Test (NHPT) and finger tapping (FT). Surface electromyography (EMG) of the bilateral abductor pollicis brevis (APB) and abductor digiti minimi (ADM) muscles was recorded. TMS was delivered with a Magstim 200 simulator connected to a figure-of-eight coil (Magstim 2nd generation, 70 mm of external diameter). Resting motor threshold (RMT) on each side and cortical mapping of APB and ADM muscles were analyzed. We also registered ipsilateral silent period (ISP) in both APB muscles, during maximal contraction. Older subjects showed worse motor performances (in terms of NHPT and FT of both hands) than younger ones ( p p p  = 0.03). In older group, APB map on the right hemisphere was significantly reduced vs the younger group ( p  = 0.021) and vs its homologous ( p  = 0.042). For ADM, no significant map differences were found between elderly and young subjects, even on the right hemisphere. ISP was significantly reduced in the elderly on both sides, in terms of duration ( p  = 0.025), peak ( p  = 0.033) and area ( p  = 0.008). Physiological aging is associated with disruption of interemispheric specialization both concerning motor cortical representation and interhemispheric interactions. This may have consequences on recovery from pathological processes and suggests that age has to be taken into account when planning therapeutic intervention aimed at restoring hand motor function.