Biomedical subjects

Canan Basar-Eroglu

Publications and source records attributed to Canan Basar-Eroglu.

5 recordsLinked to original sources

PubMed2006

Working memory related gamma oscillations in schizophrenia patients.

Recent reports show that the capability of neural networks supporting high-frequency synchronization is reduced in the brain of schizophrenia patients. Specifically, deficits in gamma activity have been shown in schizophrenia patients during perception and simple cognitive tasks. However little is known about alterations in gamma responses during complex and higher cognitive processing. The main objective of this study was to investigate modulation of event-related gamma responses in tasks varying working memory (WM) load in schizophrenia patients (N=10) and healthy controls (N=10). Gamma amplitude values were obtained for a simple choice reaction task, a low WM demand task, and a high WM demand task. During all three tasks schizophrenia patients showed significantly slower reaction times and higher error rates than controls. A gradual increase of gamma amplitudes after stimulus onset was associated with increase of WM load in controls. In contrast, high amplitude gamma oscillations remained constant regardless of task difficulty in patients. These results suggest that healthy subjects used various cognitive strategies depending on task difficulty, while schizophrenia patients needed to initiate complex cognitive processes similar to those used during processing of novel contexts or stimuli even for the simple choice reaction task with low cognitive demand.

Adult↗

PubMed2006

Voluntary control of Necker cube reversals modulates the EEG delta- and gamma-band response.

Reversible figures such as the Necker cube make up a well-known class of visual phenomena in which an invariant stimulus pattern gives rise to at least two different perceptual interpretations. Former EEG studies of our research group demonstrated a reversal-related delta response and a frontal enhancement of gamma activity during multistable perception which has been interpreted as signaling attentional top-down processes. The aim of the present study was to investigate the functional involvement of delta and gamma activity in top-down processes more explicitly by asking 21 healthy participants to bring the reversal rate under voluntary control during viewing of the Necker cube. Slowing down the reversal rate should be accomplished by focussing attention to the currently perceived alternative while speeding up should be accomplished by shifting attention as rapidly as possible from one perspective to the other. EEG was recorded from frontal, central, parietal, and occipital locations of both hemispheres. The data was analysed on the single-sweep level in the delta and gamma frequency range. The results showed that both delta response and gamma power were larger during slowing down than speeding up the reversal rate. These findings may indicate that more attentional resources have to be allocated by the cognitive system in order to prevent a reversal by means of focussed attention than to initiate a reversal by attentional shifts.

Adolescent↗

PubMed2006

Prepulse inhibition (PPI) of auditory startle reflex is associated with PPI of auditory-evoked theta oscillations in healthy humans.

The aim of the current study was to investigate the auditory-evoked theta oscillatory activity associated with prepulse inhibition (PPI) of the startle reflex in healthy humans. Concurrent electroencephalogram (EEG) and auditory startle reflex were recorded from 19 healthy controls during Pulse-Alone and Prepulse + Pulse trials with 60, 120, and 240 ms prepulse-pulse intervals. Compared to Pulse-Alone trials significant PPI of the startle reflex occurred on all Prepulse + Pulse trials and a significant startle latency reduction occurred on 60 and 120 ms Prepulse + Pulse trials. The largest evoked potentials to auditory stimuli occurred at fronto-central locations. PPI of theta oscillations occurred at frontal, central, and parietal locations. These results suggest that PPI functions not only as sensory-motor gating but also as sensory-cognitive gating since theta oscillations are involved in control of cognitive processes. Absence of significant correlations between PPI of the startle reflex and of theta oscillations at all electrode locations indicates that the two processes may be controlled by different neural mechanisms.

Acoustic Stimulation↗

PubMed2005

Theta and alpha oscillations reflect differences in memory strategy and visual discrimination performance in patients with Parkinson's disease.

The aim of the present study was to investigate alterations in brain oscillatory activity during transient intentional encoding of abstract novel shapes in patients with Parkinson's disease (PD). Combined time-frequency analyses of alpha and theta power revealed a clear dissociation between PD patients (N=10) and age-matched healthy controls (N=10). PD patients used sub-optimal stimulus encoding strategies for subsequent maintenance and recall, whereas the controls mainly used categorization processes. In contrast to controls, PD patients showed significantly less theta increase and upper alpha suppression at frontal locations and significant laterality of early posterior theta and lower-2 alpha oscillations at right posterior locations. These findings suggest that the fronto-striatal circuits participate in visual categorization processes. Furthermore, theta and alpha oscillations appear to be involved in mediating the integration processes in mnemonic networks underlying visual categorization.

Aged↗

PubMed2002

Age effects on visual EEG responses reveal distinct frontal alpha networks.

OBJECTIVES: The present study aimed to describe the effect of aging on single-trial visual alpha responses. METHODS: Visual evoked potentials were recorded at F3, Cz, P3, and O1 in 12 young (20-30-year-olds) and in 10 middle-aged adults (50-55-year-olds). Slow (7-10 Hz) and fast (10-15 Hz) alpha frequency bands were analyzed. Three parameters of single alpha responses were assessed for the 0-300 ms period after stimulus: (i) maximal single-sweep amplitude; (ii) phase-locking with stimulus, and (iii) enhancement of post-stimulus relative to pre-stimulus alpha activity. RESULTS: Ongoing alpha activity at anterior sites was larger in middle-aged subjects. Age differences in response amplitude depended on the anterior shift of ongoing alpha activity. Over fronto-central areas, the phase-locking of fast alpha responses was significantly increased, whereas the phase-locking of slow alpha responses was decreased in middle-aged compared to young adults, independently of amplitude. In contrast to slow alpha responses, frontal and occipital fast alpha responses were interrelated. CONCLUSIONS: These observations are in accordance with previous findings from the auditory modality implying that the age-related changes in frontal alpha oscillations are modality-independent. Slow and fast frontal alpha responses were affected differentially by the age, which might reflect the activations of functionally distinct alpha networks.

Adolescent↗