Biomedical subjects

Robert Roman

Publications and source records attributed to Robert Roman.

3 recordsLinked to original sources

PubMed2005

Intracerebral P3-like waveforms and the length of the stimulus-response interval in a visual oddball paradigm.

OBJECTIVE: This study investigated the possible linkage of intracerebrally recorded P3-like waveforms to the processes induced by stimulus perception or motor response formation. METHODS: Event-related potentials were recorded from 560 cerebral sites in 17 patients suffering from intractable epilepsy during visual oddball task. Potentials evoked by the target stimuli were sorted according to button-pressing response times, and the P3 waveform was analyzed both in stimulus-locked and response-locked averages, which were separately averaged for fast and slow responses. RESULTS: P3-like waveforms were identified in 180 sites in 17 patients. Three different types of P3-like waveforms, diffusely distributed within the brain, were found: (1) time-locked to the stimulus (30 sites in 11 patients); (2) time-locked to the motor response (52 sites in 13 patients); and (3) with ambiguous time relationship to stimulus and motor response (98 sites in 16 patients). CONCLUSIONS: The intracerebral P3-like waveform could represent different processes involved in performing active oddball tasks. Therefore, our results support the hypothesis that the P3 waveform registered by surface electrodes could be a heterogeneous phenomenon. SIGNIFICANCE: These results provide evidence that the P3 waveform is not only related to stimulus processing, which differs from what has been generally claimed in the literature.

Adult↗

PubMed2003

Intracerebral somatosensory event-related potentials: effect of response type (button pressing versus mental counting) on P3-like potentials within the human brain.

OBJECTIVE: To assess the contribution of different anatomical brain sites to the genesis of P3 phenomena with respect to button pressing versus mental counting tasks. METHODS: Eight intractable epileptic patients undergoing depth electrode recordings prior to their surgery participated in the study. A total of 546 cerebral sites were recorded. A standard somatosensory oddball paradigm was used. The experiment was carried out in two sessions, differing in the requested responses to targets. The averaged responses in both tasks were compared. RESULTS: After targets, two kinds of P3-like potentials were observed within different cortical sites. Task-non-specific P3 potentials were seen for both types of responses to targets. The mean amplitude of these task-non-specific P3 potentials was significantly higher in the button pressing task. The intracerebral generators of this somatosensory P3 did not differ from the known generators of auditory and visual P3s. Task-specific P3-like potentials were found much less frequently. Button pressing unequivocally generated additional P3-like potentials in the premotor cortical sites. Mental counting repeatedly evoked additional P3-like waveforms in the left-side middle and inferior temporal gyri. CONCLUSIONS: In addition to multiple intracerebral P3 generators that reflect target detection processing, other task-specific P3-like potential generators can be found in the human brain. Their activity may affect the topography and precise parameters of scalp P3 potential.

Adult↗

PubMed2002

Error processing--evidence from intracerebral ERP recordings.

Over the last decade, several authors have described an early negative (Ne) and a later positive (Pe) potential in scalp event-related potentials (ERPs) of incorrect choice reactions. The aim of the present study was to investigate the intracerebral origin and distribution of these potentials. Seven intractable epileptic patients participated in the study. A total of 231 sites in the frontal, temporal, and parietal lobes were investigated by means of depth electrodes. A standard visual oddball paradigm was performed, and electroencephalogram (EEG) epochs with correct and incorrect motor reactions were averaged independently. Prominent, mostly biphasic, ERP complexes resembling scalp Ne/Pe potentials were consistently observed in several cortical locations after incorrect trials. The most consistent findings were obtained from mesiotemporal structures; in addition to P3-like activity found after correct responses, an Ne/Pe complex was generally detected after incorrect trials. The Pe had a longer latency than the P3. Other generators of Ne/Pe-like potentials were located in different regions of the frontal lobe. The latency of the Ne was shortest in parietal, longer in temporal, and longest in frontal regions. Our findings firstly show that multiple cortical structures generate Ne and Pe. In addition to the rostral anterior cingulate cortex, the mesiotemporal and some prefrontal cortical sites seem to represent integral components of the brain's error-checking system. Secondly, the coupling of Ne and Pe to a complex suggests a common origin of Ne and Pe. Thirdly, the latency differences of the Ne across lobes suggest that the Ne is primarily elicited in posterior and temporal, and only later in frontal regions.

Adolescent↗