Biomedical subjects

Oleg A Korzyukov

Publications and source records attributed to Oleg A Korzyukov.

4 recordsLinked to original sources

PubMed2006

Habituation of auditory evoked potentials in intracranial and extracranial recordings.

Effects of stimulus repetition are investigated in short-term habituation experiments. In these experiments, trains of stimuli are applied with longer intervals of no stimulation between the trains. In scalp recordings, an amplitude and latency decrease of the auditory N100 is usually observed at the beginning of the train. This contrasts to a recent finding with intracranial recordings, exhibiting an effect on N100 amplitude, but not on its latency. In the current study, P50 and N100 were simultaneously recorded intra- and extracranially in epilepsy patients. The amplitudes of P50 and N100 decreased in both recordings, whereas the P50 latency was not significantly affected. A latency decrease was revealed for the extracranially recorded N100, but not for the intracranial N100. This dissociation between the intracranial and scalp recordings might be explained by a different sensitivity of the two measurements for N100 generators.

Adult↗

PubMed2005

Subdural recordings of the mismatch negativity (MMN) in patients with focal epilepsy.

Mismatch negativity (MMN) is elicited by discernible changes in an otherwise regular stream of auditory stimulation and reflects a pre-attentive detection mechanism. In the current study, auditory evoked potentials were recorded intracranially and electrode contacts sensitive for stimulus deviance were selected in order to further elucidate the contribution of different brain areas to MMN generation. Data were obtained from patients with frontal and temporal lobe epilepsy undergoing a presurgical evaluation by subdural and depth electrodes. In 13 of 29 patients under investigation an intracranial MMN could be observed, while in four other patients a response recovery of the N100 was revealed, mimicking an MMN. Most electrodes with an MMN signal were located in or close to the superior temporal lobe. In two patients an MMN was observed at electrode contacts over the lateral inferior frontal cortex and in one patient at a frontal interhemispheric electrode strip, giving evidence for a participation of the frontal gyrus in MMN generation. Current findings have, however, to be interpreted with caution owing to the placement and limited extension of the used electrode arrays.

Acoustic Stimulation↗

PubMed2004

Short-term habituation of the intracranially recorded auditory evoked potentials P50 and N100.

At an interstimulus interval (ISI) of 500-ms stimulus repetition leads to a strong decrease in cortical response. The functional foundation of this response suppression (or sensory gating) is yet not fully understood. Experiments on short-term habituation using the same stimulus material as sensory gating experiments and same ISI might help to elucidate the mechanisms behind the P50 suppression. Event-related potentials were recorded intracranially in epileptic patients undergoing presurgical evaluation with subdural and depth electrodes. Stimulus material consisted of trains of six clicks, with the last stimulus deviating in pitch and duration. P50 and N100 were calculated for each stimulus in the train separately and compared by analysis of variance (ANOVA). A highly significant amplitude reduction was found from the 1st to 2nd stimulus for both P50 and N100. From the 2nd to 5th stimulus no further amplitude decrease was observable. The deviating 6th stimulus led to a response recovery of both components, but the P50 elicited by the 6th stimulus was still smaller than the P50 of the 1st stimulus. Current results indicate that the P50 suppression as investigated in sensory gating experiments seems to be completed after the 2nd stimulus.

Acoustic Stimulation↗

PubMed2003

Processing abstract auditory features in the human auditory cortex.

Using electric and magnetic brain responses we tested whether violations of an abstract auditory regularity are processed in auditory cortex and whether abstract auditory regularities are retained for at least 10 s. The mismatch negativity (MMN) event-related potential and its magnetic counterpart (MMNm) were recorded to infrequent tone pairs of descending pitch (the second tone having a lower frequency than the first one) embedded in a sequence of tone pairs of ascending pitch, whereas the absolute frequency of both ascending and descending tone pairs varied on seven levels. Results showed that the dominant generators of the electromagnetic activity elicited by violations of the pitch-ascension rule lie within auditory cortex. We also found that the memory representation of pitch-ascension is retained for at least 10 s. When short trains of ascending-pitched tone pairs were followed by a silent period of 8-12 s, descending-pitched probe tone pairs elicited the MMN component when a single reminding pair with ascending pitch was presented before the probe. The reactivating effect of the reminder was similar to what has been previously shown for concrete auditory regularities, such as the constancy of tone pitch. The present results support the view that auditory cortical functions can process sensory and categorical information in a similar manner.

Acoustic Stimulation↗