The self-regulation of slow potential shifts and evoked potentials: interrelationships in response to somatosensory stimulation

More than a feeling: Scalp EEG and eye signals in conscious tactile perception

Understanding the neural basis of consciousness is a fundamental goal of neuroscience, and sensory perception is often used as a proxy for consciousness in empirical studies. However, most studies rely on reported perception of visual stimuli. Here we present behavior, high density scalp EEG and eye metric recordings collected simultaneously during a novel tactile threshold perception task. We found significant N80, N140 and P300 event related potentials in perceived trials and in perceived versus not perceived trials. Significance was limited to a P100 and P300 in not perceived trials. We also found an increase in pupil diameter and blink rate and a decrease in microsaccade rate following perceived relative to not perceived tactile stimuli. These findings support the use of eye metrics as a measure of physiological arousal associated with conscious perception. Eye metrics may also represent a novel path toward the creation of tactile no-report tasks in the future.

Cortical tuning: a function of anticipated stimulus intensity

We investigated the activation of the brain during anticipation of tactile stimuli by continuous cerebral blood flow velocity (CBFV) monitoring with bilateral transcranial Doppler sonography. A forced choice paradigm was performed where a first group of subjects (n=16) was expecting suprathreshold and a second group (n=19) was anticipating threshold tactile stimuli to the index finger after a cueing tone. During the anticipation of suprathreshold stimuli the CBFV always exhibited a significantly stronger increase in the right hemisphere than in the left, even when stimuli were anticipated at the right index finger. Conversely when stimuli at perception threshold were expected, the respective contralateral hemisphere showed a significantly stronger perfusion increase. These data show that preparatory activation of the brain during stimulus anticipation is dependant on the expected stimulus intensity.

Slow cortical potential shifts modulate P300 amplitude and topography in humans

Effects of the spontaneous slow cortical potential (SCP) shifts of the electroencephalogram (EEG) on the P300 response were investigated on ten healthy volunteers. P300 responses were recorded using an auditory oddball paradigm, where target stimuli were presented regularly after every four standard stimuli. Single event-related potential (ERP) sweeps exhibiting negative or positive SCP shifts were averaged separately. The P300 amplitude was significantly larger during negative SCP shifts. Furthermore, the topographies of P200 and P300 waves obtained during negative and positive SCP shifts showed significant differences. The results indicate that the SCP shifts in single ERP sweeps, which are considered to be correlated with the arousal or basic activity level of the cortex, explain at least part of the inter-trial variability of P300 response.