Aging-related decline in somatosensory inhibition of the human cerebral cortex

Abstract

Primary somatosensory (SI) cortical inhibition to repetitive stimuli tends to decline with increasing age. However, aging effects on the inhibition mechanism of secondary somatosensory cortex (SII) remain elusive. We aimed to study the aging-related changes of cortical inhibition in the human somatosensory system. Neuromagnetic responses to paired-pulse electrical stimulation to the median nerve were recorded in 21 young and 20 elderly male adults. Paired-pulse suppression (PPS) of SI and SII activities was estimated by the ratio of the response to Stimulus 2 to the response to Stimulus 1. Based on equivalent current dipole modeling, PPS ratios of the contralateral (SIIc) and ipsilateral (SIIi) secondary somatosensory cortices were higher in elderly than in young subjects (p < 0.001 in SIIc and p = 0.034 in SIIi). At an individual basis, a higher PPS ratio in SIIc than in SI was found in 16 (80 %) out of the 20 elderly participants; in contrast, the PPS ratios of SIIc and SI cortices were similar in young participants (p = 0.031). In conclusion, a larger PPS ratio in elderly suggests an aging-related decline in somatosensory cortical inhibition. Furthermore, compared to SI, the electrophysiological responses of SII cortex are especially vulnerable to aging in terms of cortical inhibition to repetitive stimulation.

Environmental enrichment strengthens corticocortical interactions and reduces amyloid-β oligomers in aged mice

“…It is worth noting that changes in intracortical inhibition have been associated also with physiological brain aging. However, studies in humans and animal models have shown changes in either direction (Luebke et al, 2004; McGinley et al, 2010; Schmidt et al, 2010; Marneweck et al, 2011; Cheng and Lin, 2013). On the other hand, the role of excitation has not been studied in detail.…”

“…Experimental data addressing this point in humans are contrasting. On the one hand, clinical electrophysiology show a decrease in paired-pulse suppression of magnetoencephalography (MEG) responses in the somatosensory cortex (Cheng and Lin, 2013). Similarly, a reduction in short-interval intracortical inhibition (SICI) of electromyographic (EMG) responses to pair of stimuli delivered to the cortex by transcranial magnetic stimulation (TMS) has been reported (Marneweck et al, 2011).…”

Widespread inter-ictal excitability changes in patients with temporal lobe epilepsy: A TMS/MEG study

“…Paired electrical stimulation paradigm has been applied in several different clinical populations (Frasson et al, 2001;Cheng and Lin, 2013;Hsu et al, 2013) in order to examine somatosensory cortical excitability. Increased somatosensory P35m PPI ratio was observed in TLE patients.…”

“…In other words, an ISI below 1 s would be appropriate to investigate the paired-pulse inhibition for P35m response. Several recent studies used an electrical paired pulse paradigm with ISI at 0.5 s (Wieland et al, 2008;Edgar et al, 2005;Thoma et al, 2007;Cheng and Lin, 2013;Hsu et al, 2013). Thus, a similar paradigm was used in the present study.…”

“…The electroencephalographic reactivity in auditory cortex (Lukhanina et al, 2010) or somatosensory cortex (Frasson et al, 2001) can be evaluated when corresponding paired-pulse sensory stimuli were delivered to the subjects. Some recent MEG studies have also applied paired-pulse paradigm to investigate cortical excitability in auditory Hanlon et al, 2005;Thoma et al, 2005) and somatosensory Thoma et al, 2007;Cheng and Lin, 2013;Hsu et al, 2013) cortices.…”