Biomedical subjects

J Yordanova

Publications and source records attributed to J Yordanova.

23 records · Page 2Linked to original sources

PubMed1997

Developmental changes in the event-related EEG theta response and P300.

Event-related potentials (ERPs) from 50 children (6-11 years) and 10 adults were elicited by auditory passive, and by rare target and frequent non-target stimuli, and analyzed in the time and frequency domains. The latency of the maximal theta response (or the theta frequency component of the ERP) was evaluated with respect to age and scalp topography effects. The major findings were: (1) The latency of the maximal theta response decreased with increasing age in children, although for each stimulus type and location adults had shorter latencies than the children. (2) The developmental time course of latency reduction depended on the electrode location, with the most prominent reduction occurring at 8 years at Cz, and no differences between children groups obtained for the frontal site. (3) Maximal theta response latency was strongly associated with the latency of the late parietal P400-700 (P3b) component in children. The results suggest that the developmental latency decrease in P300 processes originate from a decrease in the preceding theta-related processes and may reflect a speeding of cognitive stimulus evaluation.

Adult↗

PubMed1997

Effects of task variables on the amplitude and phase-locking of auditory gamma band responses in human.

The present study was designed to assess the effects of stimulus certainty and motor task-relevance on auditory transient 40-Hz or gamma band responses. To study the effects of these factors in a balanced design, auditory event-related potentials (ERPs) of 9 young adults were recorded in a passive listening, simple reaction task, and choice-reaction task (target tone probability = 0.5) conditions. Amplitude and phase-locking of event-related gamma activity were analyzed separately at the level of single sweeps by applying a method that allows the independent quantification of phase synchronization between consecutive single responses. Major results demonstrated that (1) During auditory stimulus processing discernible gamma oscillation bursts were observed in three time windows of the poststimulus epoch: early (0-120) ms, middle (120-250 ms) and late (250-400 ms). (2) Early gamma response amplitudes were significantly largest for highly expected motor-task stimuli, whereas the phase-locking did not depend on either of the two variables. (3) The phase-locking of late gamma responses, however, was significantly stronger to targets than to nontargets. These results indicate that auditory gamma responses are functionally involved in the processing of task variables such as stimulus certainty and motor-task relevance. It is also demonstrated that single gamma response amplitude and phase-locking have independent functional significance as being affected in a different manner by different task conditions.

Adult↗

PubMed1996

Brain theta response predicts P300 latency in children.

The present study assessed the relationship between stimulus-induced electroencephalographic (EEG) theta activity (4-7 Hz) and the endogenous component P300 of auditory event-related potentials (ERPs) using a developmental model. ERPs were recorded from 50 children (6-11 years old) for oddball target and frequent non-target stimuli and analysed in the time and frequency domains. The latency of the maximal theta response of the digitally filtered (4-7 Hz) ERPs was evaluated with respect to age and scalp topography effects. The maximal theta response latency at Cz and Pz decreased with increasing age and entirely predicted the developmental latency reduction of the parietal P400-700 (P3b) component in children.

Acoustic Stimulation↗

PubMed1996

Evoked brain rhythms are altered markedly in middle-aged subjects: single-sweep analysis.

In this study, a new method for analysis of single frequency responses was applied to compare auditory evoked potentials between young (18-30 years old) and middle-aged (50-55 years old) adults. The method was related to the evoked brain rhythmicities concept and permitted to quantify separately the magnitude, phase-locking, and enhancement against prestimulus activity of single sweeps. Thus, a constellation of three single-sweep parameters was used. No differences could be detected between the two age groups in the conventionally averaged potentials. However, significant age-related alterations were found at the level of single sweep analysis: 1) At the three midline locations (Fz, Cz, and Pz) older adults manifested theta phase-locking and enhancement that were significantly stronger than those in young adults; 2) In contrast, the alpha responses only over the frontal brain area were stronger in phase-locking and enhancement in middle-aged than in young adults, which implies that the alpha response system may be specifically related to frontal brain functioning during aging.

Acoustic Stimulation↗

PubMedDate not supplied

Coexistence of tics and hyperactivity in children: no additive at the psychophysiological level.

The objective of the present work was to study the effects of tic disorder (TD) and hyperactivity (HA) on slow cortical potentials in children with combined TD + HA symptoms. Being related to different processes of frontal lobe control over preparatory cortical activity, early and late components of the slow negative potentials (eSNP, ISNP) were examined. SNP amplitude was analyzed as reflecting the sufficiency of preparatory cortical activation; scalp distribution of SNP and relationships to reaction times were studied as revealing the efficiency of task-related region-specific activation. It was hypothesized that if the effects of TD and HA were independent, additive effects on SNP amplitudes would be observed in children with coexisting TD and HA symptoms (TD + HA). Differences in SNP scalp distribution between control and patient groups were predicted to occur mainly over the frontal brain areas. Four groups of children (n = 10/11 in each group) were studied: healthy controls, pure TD, pure attention deficit hyperactivity disorder (ADHD), and combined tic and hyperactivity symptoms. SNPs were recorded in an auditory warned reaction time task (S1-S2-RT) from 8 electrode locations. According to the results, the effects of TD and HA on the sufficiency of task-dependent cortical activation were different, with only the TD factor related to lower SNP amplitudes. Nevertheless, deviant patterns of scalp distribution were found for pure ADHD patients, which suggested an inefficiency in involving the adequate task-related areas. For TD + HA children, like pure TD, lower SNP amplitudes and similar distribution and correlation patterns were present. Thus, according to amplitude, topography, and correlation criteria, TD + HA does not appear to be a subgroup of HA disorder but seems more similar to pure tic disorder.

Acoustic Stimulation↗