Biomedical subjects

Walter R Gruber

Publications and source records attributed to Walter R Gruber.

4 recordsLinked to original sources

PubMed2006

P1 and traveling alpha waves: evidence for evoked oscillations.

The hypothesis is tested whether the P1 of the event-related potential (ERP) component behaves like an evoked, traveling alpha wave. This hypothesis is based on different kinds of evidence showing, e.g., that-after undergoing phase reorganization-frequencies in the broad alpha range become synchronized (aligned) in absolute phase and contribute significantly to the generation of the P1. We investigated data from a Stroop task in which subjects had to respond only to the color and ignore the meaning of the presented words. Analyzing topographical phase relationships expressed in terms of traveling speed (with respect to Pz as trailing site) revealed that a systematic posterior to anterior traveling pattern appeared only in the broad time window of the P1-N1 complex and in the extended alpha frequency range. The obtained findings are consistent with the oscillatory ERP model and suggest that the P1 component may be considered a manifestation of an evoked, traveling alpha wave. We assume that the P1 reflects a top-down process in a sense that traveling alpha waves control or "gate" the direction of information processing in the brain.

Adult↗

PubMed2005

Distinguishing the evoked response from phase reset: a comment to Mäkinen et al.

Mäkinen et al. [Mäkinen, V., Tiitinen, H., May, P., 2005. Auditory event-related responses are generated independently of ongoing brain activity. Neuroimage 24, 961-968] suggest the use of amplitude variance to distinguish the evoked response from phase reset. Because their data do not exhibit a drop in amplitude variance, they conclude that ERPs are generated by 'processes separate from and additive to ongoing brain activity.' We argue that this conclusion is premature because of unrealistic assumptions about the processes underlying an event-related modulation of oscillations. A realistic phase reset model has to consider at least two parameters, degree of phase reset (or 'phase concentration') and amplitude change (event-related increase or decrease in amplitude). With simulated data, we show that a variable increase in amplitude size increases amplitude variance and masks the influence of a phase reset. On the other hand, an event-related decrease in amplitude without a phase reset leads to a sharp drop in variance. Furthermore, simulation of a frequency-specific phase reset shows a drop in variance that may be too small to be detected empirically. Thus, we conclude that amplitude variance is not capable of distinguishing the evoked response from phase reset.

Brain↗

PubMed2005

Alpha phase synchronization predicts P1 and N1 latency and amplitude size.

The oscillatory phase-resetting model predicts that event-related potential (ERP) components are generated by a superposition of evoked oscillations with different frequencies. We investigate this question in a memory task in which human subjects had to retrieve a verbal label in response to the presentation of a picture. The results show that (i) evoked oscillations in the delta, theta, alpha and beta range undergo a significant phase resetting and (ii) become synchronized in absolute phase during small time windows that (iii) coincide with the latencies of the P1-N1 complex. Our conclusion is that the latencies of ERP components can be predicted at least in part by phase synchronization between frequencies.

Adult↗

PubMed2004

Theta coupling in the human electroencephalogram during a working memory task.

The role of coupling between prefrontal and temporo-parietal brain areas within the theta frequency range of the human electroencephalogram was explored in a working memory task. During encoding of visual information higher theta amplitudes were observed in the right compared to the left hemisphere. Retrieval of visuospatial and verbal information elicited a more bilateral activation pattern. These effects were accompanied by theta coupling between dorsolateral prefrontal and right posterior temporal electrode sites during encoding. During retrieval prefrontal and bilateral temporo-parietal brain areas were coupled. These results support the idea of working memory functions being dependent on distributed prefrontal-temporal networks.

Acoustic Stimulation↗