Metehan Çiçek

Brain activity during landmark and line bisection tasks.

Neglect patients bisect lines far rightward of center whereas normal subjects typically bisect lines with a slight leftward bias supporting a right hemisphere bias for attention allocation. We used fMRI to assess the brain regions related to this function in normals, using two complementary tasks. In the Landmark task subjects were required to judge whether or not a presented line was bisected correctly. During the line bisection task, subjects moved a cursor and indicated when it reached the center of the line. The conjunction of BOLD activity for both tasks showed right lateralized intra-parietal sulcus and lateral peristriate cortex activity. The results provide evidence that predominantly right hemisphere lateralized processes are engaged in normal subjects during tasks that are failed in patients with unilateral neglect and highlight the importance of a right fronto-parietal network in attention allocation.

Interhemispheric asymmetry of EEG alpha activity at rest and during the Wisconsin Card Sorting Test: relations with performance.

There are conflicting results regarding the functional asymmetry of the prefrontal cortex. Spectral power analysis of electroencephalographic (EEG) activity can provide important clues about the cortical mechanisms. In this study, interhemispheric EEG alpha power asymmetry of healthy individuals was investigated during the execution of the Wisconsin Card Sorting Test (WCST) and during rest. We analyzed alpha-1 (8.6-10.2 Hz) and alpha-2 (10.9-12.5 Hz) bands separately and found some evidence to indicate that lower and upper alpha bands reflect different cortical processes. On the other hand, greater alpha power during resting correlated with higher performance on the WCST. The lower left frontal alpha power during WCST correlated significantly with the higher WCST performance. However, greater bilateral parietal alpha power during WCST correlated with higher performance. Significant correlations between EEG activity and WCST performance were, in general, restricted to lower alpha power, both at rest and during the task. These findings are discussed with regard to attention processes reflected by lower alpha activity.

The Effect of Familial Sinistrality on the Relation between Schizophrenialike Thinking and Pseudoneglect

We have recently reported a correlation between schizophrenialike symptoms and the degree of pseudoneglect in healthy right-handers. We aimed to investigate the effect of familial sinistrality (FS) on this relation. Seventy-six healthy right-handers were divided into four groups on the basis of gender and FS. A computerized version of Corsis task was used as the visuospatial task. Subjects filled in the Magical Ideation Scale (MI), which asked for delusionlike beliefs, and performed the Corsis task using each hand. Performance of both hemispaces was separately evaluated. In all groups, performance of the left hemispace was better than that of the right hemispace and FS+ subjects performed better than FS- subjects. When the right hand was used, performance was correlated to MI scores only for FS- groups. Findings suggest that the correlation between right-sided neglect and proneness to schizotypy in normal right-handers is affected by FS.

Cognitive control of a simple mental image in patients with obsessive–compulsive disorder

The nature of obsessions has led researchers to try to determine if the main problem in obsessive-compulsive disorder (OCD) is impaired inhibitory control. Previous studies report that the effort to suppress is one of the factors that increase the frequency of obsessive thoughts. Based on these results and those of the present study that suggest inferior parietal lobe (IPL) abnormality in OCD and findings of a recent study that reported the importance of the right posterior parietal cortex in cognitive control of a simple mental image, the present cognitive control paradigm study aimed to determine whether there is a difference in brain dynamics between OCD patients and non-obsessive controls while performing tasks that necessitate cognitive control of a simple mental image, and whether the right posterior parietal region is one of the regions in which a difference in activity between the OCD patients and controls would be observed. Functional brain imaging was performed while the participants attempted to suppress, imagine, or manipulate a mental image. The general linear model showed that there was a main effect of group and main effect of task. Accordingly, in all contrasts (suppression minus free-imagination, erasing minus free-imagination, and imagination minus free-imagination), the right IPL, right posterior cingulate cortex, and right superior frontal gyrus activity were lower in the OCD patients than in the healthy controls. These results and the observed correlations between activity levels, and symptom and subjective performance scores are discussed. In conclusion, the results of the present study and those of previous studies suggest that the main problem in OCD might be difficulty activating the right frontoparietal networks during tasks that require cognitive control, which might result in the intrusiveness of obsessive thoughts.

Pseudoneglect of Males and Females on a Spatial Short-Term Memory Task:

The effect of sex on the phenomenon of pseudoneglect was assessed in 60 male and 61 female right-handed subjects using a modified form of Corsis block-tapping test. A significant right-lateralized pseudoneglect for both sexes was found, and the level of pseudoneglect strongly correlated with neglect in the right hemispace. Men were significantly more accurate in the left hemispace than women, whereas no difference was seen between the sexes in the right hemispace. Although we found some indirect evidence from which to infer that the mens brain may be functionally more lateralized than the womens for this spatial task, there was no significant difference between the sexes in correct responses for the left hemispace, i.e., right pseudoneglect. Therefore, the results suggest that pseudoneglect phenomenon can be partly explained by a functional asymmetric feature of the brain, and the other factors probably play a role in producing the similar patterns of asymmetric perception of space in males and females.

Neural Networks for Time Perception and Working Memory

Time is an important concept which determines most human behaviors, however questions remain about how time is perceived and which areas of the brain are responsible for time perception. The aim of this study was to evaluate the relationship between time perception and working memory in healthy adults. Functional magnetic resonance imaging (fMRI) was used during the application of a visual paradigm. In all of the conditions, the participants were presented with a moving black rectangle on a gray screen. The rectangle was obstructed by a black bar for a time period and then reappeared again. During different conditions, participants (n = 15, eight male) responded according to the instructions they were given, including details about time and the working memory or dual task requirements. The results showed activations in right dorsolateral prefrontal and right intraparietal cortical networks, together with the anterior cingulate cortex (ACC), anterior insula and basal ganglia (BG) during time perception. On the other hand, working memory engaged the left prefrontal cortex, ACC, left superior parietal cortex, BG and cerebellum activity. Both time perception and working memory were related to a strong peristriate cortical activity. On the other hand, the interaction of time and memory showed activity in the intraparietal sulcus (IPS) and posterior cingulate cortex (PCC). These results support a distributed neural network based model for time perception and that the intraparietal and posterior cingulate areas might play a role in the interface of memory and timing.

Default Mode Network Connectivity Differences in Obsessive-compulsive Disorder

Recent evidence suggests that the brain intrinsic activity during rest might be as significant as task evoked activities and consumes considerable energy linked to neural signaling processes. We performed an fMRI study recently aiming to compare the differences in brain activity between patients with obsessive-compulsive disorder and healthy volunteers during a simple suppression paradigm. We hypothesized that the patients with obsessive-compulsive disorder would show default mode network (DMN) connectivity dissociations from healthy individuals. OcD patients had higher connectivity (p < 0.05) than controls between right inferior parietal lobe (IPL) and left ventral medial prefrontal cortex (MPFC).

Frontal and posterior ERPs related to line bisection.

The aim of this study was to investigate the dynamic nature of the cortical visuospatial attention processes during the line bisection test, which is sensitive to perceptual asymmetries. EEGs of 26 normal volunteers were recorded during the administration of a computerized line bisection test, which requires participants mark the midline of lines using a mouse. Two event-related potentials subsequent and time locked to the line presentations, namely, P300 and a positive slow wave, were obtained. Findings suggested that both potentials were related to the test performance, and the right hemisphere was more active. Analysis suggested a right parietotemporal and superior parietal locus for the P300 and right prefrontal activity for the positive slow wave. A dynamic asymmetrical activity was identified, such that after primary visual perception, spatial processing is then initiated in the right parietotemporal cortex and then proceeds to the right prefrontal cortex.

A comparative analysis of functional connectivity data in resting and task-related conditions of the brain for disease signature of OCD

Obsessive Compulsive Disorder (OCD) is a frequent, chronic disorder producing intrusive thoughts which results in repetitive behaviors. It is thought that this psychological disorder occurs due to abnormal functional connectivity in certain regions of the brain called Default Mode Network (DMN) mainly. Recently, functional MRI (FMRI) studies were performed in order to compare the differences in brain activity between patients with OCD and healthy individuals through different conditions of the brain. Our previous study on extraction of disease signature for OCD that is determining the features for discrimination of OCD patients from healthy individuals based on their resting-sate functional connectivity (rs-FC) data had given encouraging results. In the present study, functional data extracted from FMRI images of subjects under imagination task (maintaining an image in mind, im-FC) is considered. The aim of this study is to compare classification results achieved from both resting and task-related (imagination) conditions. This research has shown quite interesting and promising results using the same classification (SVM) method.

Detection of obsessive compulsive disorder using resting-state functional connectivity data

Obsessive Compulsive Disorder (OCD) is a serious psychological disease that might be affiliated with abnormal resting-state functional connectivity (rs-FC) in default mode network (DMN) of brain. In this study it is aimed to discriminate patients with OCD from healthy individuals by employing pattern recognition methods on resting-state functional connectivity (rs-FC) data. For this purpose, two different feature extraction approaches were implemented. In the first approach the rs-FC fMRI data were subsampled and then the dimensionality of the subsampled data was reduced using subspace transforms. In the second approach, feature vectors having already low dimensions were obtained by measuring similarities of the rs-FC data of subjects to the separate means in OCD and healthy groups. Afterwards the healthy and OCD groups were classified using Support Vector Machine (SVM). In order to obtain more reliable performance results, the Double LOO-CV method that we proposed as a version of Leave-One-Out Cross Validation (LOO-CV) was used. Quite encouraging results are obtained when the features extracted using similarity measures are classified by SVM.