Erhan Nalçaci

The relationship between handedness and fine motor performance.

The aim of this study was to re-investigate the relationship between handedness and asymmetry in hand performance, and the sex difference in motor asymmetry. Three-hundred and ten medical students volunteered as subjects. Handedness was assessed by a 13-item questionnaire adapted from Chapman and Chapman. Fine motor performance was measured using a finger tapping task. In this task, subjects were required to tap as rapidly as possible with their index finger on a mouse button for a period of 10 s. There was a significant correlation between handedness scores and the scores of the finger tapping task. In the total sample, the correlation between hand speed and the handedness score indicated that the distribution of hand preference is associated with left hand speed, but not right hand speed. Results confirmed that right-handed females tend to have more asymmetric motor function than right-handed males.

Aspects of foot preference: differential relationships of skilled and unskilled foot movements with motor asymmetry.

In this research different aspects of foot preference were examined in 50 participants. The relationship between foot preference, hand preference, and hand/foot-tapping performance was analysed in detail. For foot preference, a practical behavioural test consisting of 14 daily foot movements was developed. After statistical analysis, five items were dropped. The test–retest reliabilities of the nine-item foot preference test and the foot-tapping task were found to be high. The factor analysis indicated a two-factor structure (skilled and unskilled foot movements). Foot preference in skilled and unskilled movements was correlated with hand preference and foot/hand-tapping speed. This correlation was found to be higher in skilled movements than in unskilled movements. Additionally, foot preference for skilled movements was strongly lateralised. The results indicate that the motor control of fine movements is similar for upper and lower limbs. The fact of lateralisation indicates that skilled and unskilled foot movements utilise different pathways. We propose that the asymmetrical lateral (corticospinal) pathway controls skilled movements while the medial pathways control unskilled movements. We therefore suggest that both skilled and unskilled foot tasks should be evaluated separately in order to assess foot preference.

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.

Visual evoked potential interhemispheric transfer time in different frequency bands

OBJECTIVE Visual evoked potentials (VEP) have been used to estimate interhemispheric transfer time (IHTT). However, the complex wave of VEP is most probably formed by different generators of neural populations that act through different frequency channels. If the main peaks of VEP are established by different types of generators, which can also be connected to each other by a different type of callosal fibres, we would be able to estimate a wide range of various IHTT by measuring the latency between time-locked peaks of narrow band-pass filtered VEP. This research aimed to test this hypothesis. METHODS Nine right-handed men were presented with a reversal of a checkerboard pattern as stimuli at RVF or LVF, and EEG was recorded at O1, O2, P3, P4. The grand-averaged VEPs were transformed to the frequency domain by means of the fast Fourier transform to obtain the amplitude frequency characteristics. Band-pass filters were chosen adequately, according to tuning frequencies indicated by clear peaks in the amplitude frequency characteristics. The chosen band pass filters (4-8 Hz, 8-15 Hz, 15-20 Hz, 20-32 Hz) were applied to the VEP of the subjects, and 4 different components of VEPs for each VEP were obtained. The latency of P100 and N160 of unfiltered VEP was measured. In the band-pass digital filter applied VEPs, positive and negative peaks, which are consistent with P100 and N160, were measured for each subject. Latency differences between hemispheres for digitally unfiltered and filtered VEPs were computed to estimate IHTT. RESULTS In the different frequency bands, different IHTTs were estimated, ranging from 3 ms to 30 ms. Approximately 16 ms for theta band, 11 ms for alpha band, 6 ms for 15-20 Hz and 3 ms for 20-32 Hz bands were found. CONCLUSIONS Our findings support the hypothesis which states that unfiltered VEPs provide us with only a rough estimation of IHTT. Also, they are consistent with anatomical findings that describe callosal fibres of varying dimensions, predicting various velocities between hemispheres.

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.

Corpus callosum has different channels for transmission of spatial frequency information

Many studies suggest that separate retinocortical channels with different conduction speeds transmit the information about high and low spatial frequencies (SF). Similarly, separate callosal channels may be responsible for the transfer of different SFs. To test this hypothesis, interhemispheric transfer time (IHTT) was estimated using visual evoked potentials (VEPs) elicited by reversal of different SF checkerboard patterns, which were presented either in the right or left visual hemifield. VEPs were recorded from homologous occipital and parietal leads in 11 subjects. The P100 latencies obtained from directly stimulated hemispheres were defined as retinocortical conduction times. The difference in P100 latencies obtained from directly and indirectly stimulated hemispheres was defined as IHTT (i.e., contralateral P100 latency values subtracted from the ipsilateral latency values). The results, showing faster retinocortical transfer for low SF than for high SF, and the shortest transfer time at parietal leads only for low SF, indicate that the presented stimuli are transferred on separate retinocortical channels. Concerning the interhemispheric transfer (VEP-IHTT), faster right-to-left than left-to-right transfer for both low and high SF stimuli was found, which is in congruence with previous studies. Most important however, the VEP-IHTT was faster for low SF than high SF. These different interhemispheric transfer speeds support the hypothesis that transferring low SF, compared with high SF information, relies on larger callosal fibers. Thus, we conclude that indeed distinct callosal channels respond selectively to the SF content of visual stimuli.

Directional Preferences in Turning Behavior of Girls and Boys

Turning biases in humans and animals are known to be related to dopaminergic asymmetry between the brain hemispheres. A laboratory method, in which turning preference was evaluated, was adapted based upon the turning of the subject toward a particular sound in a square room. One of the aims of this study was to investigate the reliability of this method with children, and the other aim was to research the turning preference in boys and girls. 31 children between 7 and 13 yr. old volunteered as subjects, and 17 subjects were retested. The subjects tended significantly to turn leftward (60.1%), and fewer girls (53.7%) turned to the left than boys (66.2%). The correlation between the test and the retest was significant (r = .79, p < .01). Most studies have indicated that humans in childhood and adulthood exhibit left-turning preference, but conflicts between the results obtained on different types of rotation tasks have suggested that hemispheric dopaminergic activity might affect preference. That needs study.

Evaluation of cognitive slowing in OCD by means of creating incongruence between lexicon and prosody

Studies indicate that patients with obsessive-compulsive disorder (OCD) have slowing in cognitive processing, especially in the presence of a conflict. This study aimed to determine whether decision and motor times in OCD patients were affected by manipulating the congruence/incongruence of lexical and prosodic aspects of commands. An experimental paradigm was designed to simulate a situation that can trigger anxiety and obsessions in OCD patients. Commands with or without a conflict, that is, an incongruence between lexical and prosodic aspects, were given to the participants. Decision time, motor time and errors were the main parameters of the experiment. The control group had significantly faster decision times than the OCD group in response to both conflicting and non-conflicting commands. The OCD patients demonstrated higher trait anxiety, while Stroop interference and state anxiety were not significantly different between the groups. These results suggest that OCD patients experience slowing in their response times, regardless of whether the stimuli are conflicting or not.

Time-frequency analysis of visual evoked potentials for interhemispheric transfer time and proportion in callosal fibers of different diameters

Abstract.This study is an extension of the experimental research of Nalçacı et al., who presented 16 subjects with a reversal of checkerboard pattern as stimuli in the right visual field or left visual field and recorded EEG at O1, O2, P3, and P4. They applied the chosen bandpass filters (4–8, 8–15, 15–20, 20–32 Hz) to the VEPs of subjects and obtained four different components for each VEP. The first aim of this study is to improve the previous report using some methods in time-frequency domain to estimate interhemispheric delays and amplitudes in a time window. Using the improved estimates of interhemispheric delays, the second aim is to estimate the proportion of callosal fibers of different diameters that are activated by visual stimuli by comparing amplitudes of VEPs in different frequency bands. If the relation between frequency components of VEP and delays for callosal fibers of different dimension were reliable, it would give us an opportunity to deal with amplitude of bandpass-filtered VEPs in order to see approximately the proportion of these fibers activated by a certain stimulus. By using frequency-dependent shifts in time and maximizing the cross correlation of direct VEP (DVEP–VEP obtained from contralateral hemisphere)–indirect VEP (IVEP–VEP obtained from ipsilateral hemisphere) pairs in the time-frequency domain, we examined the delay not only at P100 and N160 peaks but along a meaningful time interval as well. Furthermore, by shifting back the IVEP according to the delay estimated at each time window, both the amplitudes and energies of the synchronized DVEP–IVEP pairs were compared at the chosen frequency bands. The percentages of IVEPs at each band was then examined further in conjunction with the distribution of axon diameters in the posterior pole of the CC, questioning the relation between the distributions of the axon diameters and activations at each band. We established an energy definition to express the activation in the fibers. When the energy percentages of IVEPs in theta and alpha were totaled, they were found to be between 76.2% and 81.6%, which is close to the value 74–77% for fibers of 0.4–1 μm in diameter obtained from anatomical study of human CC. The sum of energy percentages in the beta1 and beta2 bands was between 20.1% and 24.2%, which probably reflects the proportion of activation of callosal fibers 1–3 μm in diameter.