Abstract
The brain builds up expectations to future events based on the patterns of past events. This function has been studied extensively in the auditory and visual domains using various oddball paradigms, but only little exploration of this phenomenon has been done in the somatosensory domain. In this study, we explore how expectations of somatosensory stimulations are established and expressed in neural activity as measured with magnetoencephalography. Using tactile stimulations to the index finger, we compared conditions with actual stimulation to conditions with omitted stimulations, both of which were either expected or unexpected.Our results show that when a stimulation is expected but omitted, a time-locked response occurs ∼135 ms subsequent to the expected stimulation. This somatosensory response to “nothing” was source localized to the secondary somatosensory cortex and to the insula. This provides novel evidence of the capability of the brain of millisecond time-keeping of somatosensory patterns across intervals of 3000 ms.Our results also show that when stimuli are repeated and expectations are established, there is associated activity in the theta and beta bands. These theta and beta band expressions of expectation were localized to the primary somatosensory area, inferior parietal cortex and cerebellum. Furthermore, there was gamma band activity in the right insula for the first stimulation after an omission, which indicates the detection of a new stimulation event after an expected pattern has been broken.Finally, our results show that cerebellum play a crucial role in predicting upcoming stimulation and in predicting when stimulation may begin again.
Highlights
Conceiving of the brain as a passive recipient of stimulation, and as an active predictor of future stimulation dates back to at least Helmholtz (1867)
The results showed that Repeated and First Stimulation were very similar with the first component occurring contralaterally to the stimulated hand at 56 ms over the somatosensory cortex (SI-component), which was followed by a second bilateral component at 135 ms over the secondary somatosensory cortices (SIIcomponent) (Fig. 2AB)
Since it is potentially possible that the theta, beta and gamma band increases for Repeated relative to First Stimulation are due to refractory activity from the preceding stimulation, we examined this possibility by calculating the temporal spectral evolution of these frequency bands (Salmelin and Hari, 1994) (Fig. 5E)
Summary
Conceiving of the brain as a passive recipient of stimulation, and as an active predictor of future stimulation dates back to at least Helmholtz (1867). In support of this notion, a seminal electrophysiological experiment (Näätänen et al, 1978)) demonstrated that the auditory cortex generates a characteristic response to deviant sounds in a sequence of otherwise standard sounds. This response, which manifested as a time-locked increased negativity in the electroencephalogram (EEG) from about 130 ms to about 300 ms after stimulus onset of the deviant stimuli over fronto-central electrodes, was coined the MisMatch Negativity (MMN). The neural generators of the auditory MMN have been localized to the primary and secondary auditory cortices (Alho, 1995)
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