Electrophysiology

Mindfulness is known to positively impact behavioral and electrophysiological outcomes of inhibitory executive control following long-term practice. For example, increased accuracy and decreased reaction time, as well as neural markers of increased inhibitory processing. More evidence is emerging demonstrating increased inhibitory control following shorter-term interventions ranging from 3 days to less than 8 weeks. However, findings following single, brief (>1 hour) remain mixed. The current study measured behavioral and EEG changes on a Stroop task in 40 college students following either a 30-minute guided mindfulness meditation or audiobook listening. A breath-counting task (objective measure of mindfulness) was administered to capture the effectiveness of the intervention. Results showed the mindfulness group had trending increased accuracy on the breath-counting task post-intervention compared to controls. Equivalent performance was seen across all Stroop trial conditions regardless of group. Regarding the EEG findings, a between-group effect emerged for congruent N2 voltage at P4 and incongruent N2 voltages at FC1 indicating the mindfulness group had reduced negative voltages across both time points. There was a within-subjects x group interaction for incongruent P3b voltage at Pz; MG increased while controls decreased (opposite of what was expected). This study provides partial evidence for a single, 30-min mindfulness induction in producing a more mindful awareness compared to an audiobook control group. Findings regarding enhanced inhibitory processing following the mindfulness intervention are mixed. Contrary to expectations, our findings implicate the effectiveness of a 30-min mindfulness induction in increased resource recruitment for evaluating incongruent words in absence of behavioral effects.

This dissertation examined the neural correlates of auditory perception, attention
and expectation in three experiments. Experiment 1 analyzed neural correlates of auditory
perception and expectation in an electroencephalography (EEG) experiment using a
temporally perturbed metronome to establish an expectation for auditory events, then
violate and reestablish that expectation. High frequency evoked (phase-locked) gamma
band activity (GBA) was observed to follow the onset of tones whereas induced (nonphase-
locked) GBA reached maximum power simultaneously with the occurrence oftone
onset. Moreover, the latency of induced GBA was perturbed after an expectancy violation
and relaxed back into synchrony as the expectation was reestablished.
Experiment 2 was a methodological study to compare two functional magnetic
resonance imaging (fMRJ) scanning techniques and assess their influence on auditory
processing. Subjects passively listened to isochronous tone sequences at three rates while
sparse or continuous scanning was employed. Sparse and continuous scanning was observed to yield comparable fMRI data, however, continuous scanner notse was
observed to perturb known EEG evoked response potentials. Moreover, high frequency
evoked activity, as identified by spectral analysis, was attenuated in the presence of
continuous fMRl noise.
Experiment 3 was conducted to study auditory expectancy and attention. First,
subjects were tested behaviorally to determine their ability to tap the beat of ten highly
syncopated patterns. Subjects were asked to return for one EEG and one fMRl session. In
these sessions, they were instructed to attend to a syncopated pattern, mentally rehearse
the pattern, and then reproduce the pattern. During the control condition, subjects heard
the auditory patterns, however, they were instructed to study a list of words, remember
the words during the retention interval, and then recall as many words as possible. Brain
activity was localized to frontal and auditory regions when attending to the patterns and
occipital-auditory areas when attending to the words. Evoked activity was shown to
reflect the subject's anticipation of the beat and was attenuated when ignoring the
auditory stimulus.
Taken together, these results suggest that GBA indexes auditory perception,
attention and expectation. The current results suggest that attention and task engagement
may elicit stronger neural phase locking.

The experiments in this dissertation were designed to produce a systematic characterization of the neuroelectric and neuromagnetic correlates of isochronous tone stimulation and simple rhythmic movements over a broad range of rates. The goal was to determine how the cortical representation of rhythm changes with rate, which would provide insight into known rate-dependent differences in perceptual and coordinative abilities. Fundamental transitions in the composition of the auditory and motor responses were hypothesized to occur within the parameter ranges studied here, including the attenuation of major response components and a shift from discrete transient activity at low rates to continuous steady-state activity at high rates. The auditory responses were studied in separate electroencephalography (EEG) and magnetoencephalography (MEG) experiments with stimulation rates ranging from 0.5 to 8Hz. In both studies, a transition from a transient to a continuous steady-state representation of the tone sequence occurred near 2Hz. In addition, an N1m component of the transient responses disappeared at rates near 8Hz, which may indicate the border beyond which tones are no longer distinct since the response is known to be an index of novelty in the auditory environment. Moreover, in a result important for understanding how evoked activity interacts with activity already present in the cortex, the phase of ongoing 40Hz rhythms is shown to affect the amplitude of the auditory evoked 40Hz response. Rhythmic finger movement was studied using a continuation paradigm in two EEG and MEG experiments at movement rates from 0.5 to 2.5Hz. Major findings included the disappearance of activity associated with movement planning and initiation at rates above 1Hz, suggesting a transition into a steady-state motor response in which there is less direct control of individual movements by the cortex. In addition, the neural correlates of synchronization and continuation were compared, with the results showing a similar cortical organization of metronome-paced and self-paced movements. The attenuation of major response components and the development of continuous steady-state activity within the present parameter ranges indicate rate-dependent changes in the cortical representation of simple rhythms, which are proposed here to relate to known rate-dependent behavioral differences in more complex coordinative environments.