Evoked potentials (Electrophysiology)

Event-related potentials were studied to explore the effects
of novelty, along the dimension of categorizability, on P-300
amplitudes and latency. The effects of spatial and verbal
information processing on P-300 amplitude and latency as well as
the effects of novelty and processing mode on incidental learning
were also studied. No significant P-300 data was demonstrated.
A forced choice recognition memory test did show significant
differences between the spatial and verbal tasks and between the
three different stimulus types.

Visual and auditory evoked potentials were studied in a
selective attention paradigm similar to that of Posner and
Boies (1971) wherein a visual letter-matching task was
interrupted by auditory probes on selected trials. A neural
inhibition model of the P300 component was proposed which
generated the hypothesis that the P300 component in response
to auditory probes would be greatest in amplitude to probes
which occurred between the two to-be-remembered test letters
and smaller in amplitude to probes which occurred before the
presentation of the first test letter. General support for
the neural inhibition model was found, however, systematically
shifting prestimulus baselines were also observed
within these time intervals thereby raising the possibility
that the differences in P300 amplitudes were due to nonspecific
changes in the general arousal level of the subject.
It was also found that instruction-induced differences in
response speed affected the amplitude of the evoked potential
components in a way which could most parsimoniously be
attributed to shifts in general arousal.

Visual evoked potentials were elicited by tachistoscopic
presentation of familiar (real words) and novel (pseudowords)
verbal stimuli to young and elderly adults. The amplitude
and latency of the P300 component did not differ significantly
for any of the experimental conditions. Excessive
noise in the averaged waveforms, most likely due to eye
and motor contaminants, may have been partly responsible
for the failure to confirm the hypotheses.

A signal detection experiment tested the assumption
that the results of Hillyard, Squires, Bauer and Lindsay
(1971), who found a significant late positive component
(LFC) of the averaged evoked potential only in the hit
category, were due to the response set of their Ss and
not to any unique associations of the LPC with the hit
category as interpreted by them. Phase 1 of the present
study was basically a replication of Hillyard's study.
In Phase 2 incorrect responses were punished by an
unpleasant feedback device designed to place more equal
relevance on signal and non-signal trials. Significant
LPCs appeared in both signal and non-signal brain waves
under both phases indicating that the LPC is not contingent
on any particular response category as Hillyard reported,
but may instead reflect the relevance of the category
to the experimental task as it is perceived by the S.

Facial recognition memory is a specialized system in the human brain, with an effect of familiarity playing a role in the brain activations involved. Previous studies examining the familiar face processing system have used college-aged subjects. However, memory disorders, like those associated with Alzheimer's disease, typically affect adults over sixty. In an attempt to reveal possible differences between young and older adults', two different age groups were subjected to fMRI analysis while viewing face images with varying familiarity (family, famous and novel). The result showed a significant difference in activations for various cortical areas including the precuneus, cingulate cortex, and fusiform gyrus. Among the differences, an overall trend of greater activation in the left hemisphere for younger subjects compared to the older group was revealed. The results have implications for the study of memory disorders afflicting older adults, like Alzheimer's disease.

The P300 (P3) component of the auditory Event-Related Potential (ERP) waveform is a sensitive and clinically useful marker of central nervous system impairment. The amplitude (in muV) and latency (in ms) of the P3 component of the auditory ERP were used in the present study to investigate differences between HIV-asymptomatic, HIV-symptomatic, and HIV-negative control adult (18--35 years old) women under three different task conditions. Results indicated that P3 amplitude measures were consistently greater in controls than in the asymptomatic and symptomatic groups for all task conditions and at all electrode locations, suggesting that the available level of attentional resources are reduced similarly in both symptomatics and asymptomatics. P3 latency measures revealed that processing speed by asymptomatics is more similar to controls than it is to symptomatics, indicating that speed of processing is compromised in symptomatics, and possibly, to a lesser degree in asymptomatics.

The ability to coordinate rhythmic finger movement with a metronome is constrained by both the target timing relation and the rate of coordination. For slow metronome rates (<2 Hz), subjects are able to both syncopate (in between successive beats) and synchronize (on each beat) with the metronome. At faster rates, however, syncopation becomes unstable and subjects spontaneously switch to synchronization in order to maintain a 1:1 stimulus/response relationship. No switches are observed if subjects start in synchronization, indicating it is an inherently more stable mode of coordination. Patterns of brain activity associated with transitions from syncopation to synchronization as well as synchronization only were examined as the metronome rate was increased from 1.0 to 2.75 or 3.0 Hz. Significant differences in the power of the coordination frequency component of event-related potentials (EEG) as well as the MEG beta (15--30 Hz) rhythm were observed when brain activity associated with syncopation was compared to that accompanying synchronization. These differences were focused over left central and centro-parietal areas and the direction of difference in both cases suggests that syncopation is associated with stronger activation of contralateral sensorimotor cortex. Similar results were found when subjects only imagined performing each mode of coordination at an increasing rate, indicating that differences in signal power at least partially reflect neural processes associated with motor planning and preparation independent of overt execution. Consistent with these findings, functional MRI revealed syncopation to be accompanied by significantly more activity in a wide array of cortical (e.g., premotor, prefrontal) and subcortical (basal ganglia, cerebellum) areas known to play a role in motor planning and/or timing of behavior. Whereas the neuromagnetic auditory response decreased as function of coordination rate, the motor evoked response remained approximately constant. This was true both when subjects syncopated and synchronized but may reflect changes in auditory-motor integration near movement rates that induce transitions in the former case. A control experiment examined only self-paced movement and showed a second neuromagnetic motor 'readiness' response that was strongly attenuated for rates above 1.0 Hz. This may signify a decreased need for the planning of motor behavior at faster rhythmic rates.