Exercise effects on early cortical somatosensory and nociceptive processing in the human brain

Abstract

Functional brain imaging methods were utilized to investigate early cortical somatosensory and nociceptive processing and how exercise may affect these processes. Study I examined automatic somatosensory change detection system with EEG and exercise effects on this system utilizing data collected from monozygotic twin pairs who were discordant in their long-term exercise status within pair. The results of Study I showed that long-term exercise selectively modulates specific early somatosensory electrophysiological brain responses as the inactive co-twins showed stronger somatosensory mismatch response (SMMR) compared to their active co-twins. Study II investigated somatosensory automatic change detection system with magnetoencephalography (MEG) using SMMR experiment design with electrical and tactile stimulation. The results of Study II demonstrated the feasibility of both tactile and electrical stimulation in reliably detecting SMMR with MEG. Furthermore, these results support previous studies indicating the involvement of the primary and secondary somatosensory cortices in the somatosensory automatic change detection system. Study III examined which uni- and bilateral cortical areas are involved in early somatosensory automatic processing with MEG utilizing innocuous and nociceptive electrical stimulations. The results of Study III demonstrated spatial and temporal dissociation in brain activations following electrical stimulation to slightly diverging hand areas. Study IV investigated the effects of acute exercise on cortical nociceptive processing and excitability in the sensorimotor cortex. The results of Study IV revealed modulation in the oscillatory nociceptive processing over sensorimotor cortex after acute exercise. This modulation was observed in the ~20 Hz motor cortex rhythm as the stimulation-induced suppression was stronger followed by a tendency towards weaker rebound. Overall, the findings in this dissertation demonstrate interaction between exercise and cortical somatosensory and nociceptive systems. Further research is necessary for better understanding of the mechanisms underlying this interaction and linking this information to designing optimal rehabilitation paradigms.