Biomedical subjects

Ioannis Evdokimidis

Publications and source records attributed to Ioannis Evdokimidis.

14 recordsLinked to original sources

PubMed2006

Smooth pursuit eye movements in 1,087 men: effects of schizotypy, anxiety, and depression.

Individuals with schizotypal personality disorder or high scores in questionnaires measuring schizotypy are at high risk for the development of schizophrenia and they also share some of the same phenotypic characteristics such as eye-tracking dysfunction (ETD). The question arises whether these individuals form a distinct high-risk group in the general population or whether schizotypy and ETD co-vary in the general population with no distinct cutoff point for a high-risk group. A large sample of military conscripts aged 18-25 were screened using oculomotor, cognitive and psychometric tools for the purposes of a prospective study on predisposing factors for the development of psychosis. Schizotypy measured using the perceptual aberration scale (PAS) and the schizotypal personality questionnaire (SPQ), anxiety and depression, measured using the Symptom Checklist 90-R, had no effect on pursuit performance in the total sample. Small groups of individuals with very high scores in schizotypy questionnaires were then identified. These groups were not mutually exclusive. The high PAS group had higher root-mean-square error scores (a quantitative measure for pursuit quality) than the total sample, and the high disorganized factor of SPQ group had lower gain and higher saccade frequencies in pursuit than the total sample. The presence of significant differences in pursuit performance only for predefined high schizotypy groups favors the hypothesis that individuals with high schizotypy might present one or more high-risk groups, distinct from the general population, that are prone to ETD as that observed in schizophrenia.

Adolescent↗

PubMed2006

Effect of schizotypy on cognitive performance and its tuning by COMT val158 met genotype variations in a large population of young men.

BACKGROUND: Mirroring schizophrenia, specific dimensions of schizotypy are related to cognitive dysfunction. The relation of schizotypy and state psychopathology to cognitive performance and its link to catechol-O-methyltransferase (COMT) val(158) met genotype variations was studied in a large sample of young men. METHODS: State psychopathology and schizotypy were assessed with self-rated questionnaires. Cognitive performance was assessed with tests of reasoning ability, sustained attention, and verbal and spatial working memory. Subjects were genotyped for the val(158) met polymorphism of the gene for COMT (low enzymatic activity met/met, intermediate met/val, and high val/val). RESULTS: The val/val group had higher scores in measures of state psychopathology as well as negative and disorganized schizotypy dimensions, whereas there was no effect of COMT genotype on cognitive performance measures. Structural equation modeling showed that cognitive performance accuracy but not speed decreased with increasing negative schizotypy, increased with increasing paranoid schizotypy, and was not affected by state psychopathology. Increasing val loading resulted in a dose-dependent increase in the factor loading for the relation between negative schizotypy and cognitive performance accuracy. CONCLUSIONS: Different schizotypal phenotypes had opposing relations to cognitive performance in the population. COMT genotype modulated the relation between the negative schizotypal phenotype and cognitive performance.

Adolescent↗

PubMed2006

"Motor oblique effect": perceptual direction discrimination and pointing to memorized visual targets share the same preference for cardinal orientations.

In previous studies we observed a pattern of systematic directional errors when humans pointed to memorized visual target locations in two-dimensional (2-D) space. This directional error was also observed in the initial direction of slow movements toward visual targets or movements to kinesthetically defined targets in 2-D space. In this study we used a perceptual experiment where subjects decide whether an arrow points in the direction of a visual target in 2-D space and observed a systematic distortion in direction discrimination known as the "oblique effect." More specifically, direction discrimination was better for cardinal directions than for oblique. We then used an equivalent measure of direction discrimination in a task where subjects pointed to memorized visual target locations and showed the presence of a motor oblique effect. We finally modeled the oblique effect in the perceptual and motor task using a quadratic function. The model successfully predicted the observed direction discrimination differences in both tasks and, furthermore, the parameter of the model that was related to the shape of the function was not different between the motor and the perceptual tasks. We conclude that a similarly distorted representation of target direction is present for memorized pointing movements and perceptual direction discrimination.

Adult↗

PubMed2006

Mixed handedness is associated with the Disorganization dimension of schizotypy in a young male population.

Within the ASPIS (Athens Study of Psychosis Proneness and Incidence of Schizophrenia) we sought out to examine in accordance with previous reports if a deviation from dextrality is associated with an augmented endorsement of self rated schizotypal personality traits in a large population of 1129 young male army recruits. Schizotypal traits were assessed using the Schizotypal Personality Questionnaire and hand preference membership was determined by applying stringent criteria derived from the Annett Handedness Questionnaire and the Porac-Coren questionnaire of lateral preferences. By adopting three different definitions of hand preference membership, we confirmed an association between mixed handedness and increased schizotypal personality traits, and in particular with Disorganization schizotypy that encompasses aspects of self perceived difficulties in verbal communication. Non-verbal cognitive ability, as indexed by measurement of non-verbal IQ, sustained attention and working memory was not associated with hand preference. We argue that a deviation from normal cerebral lateralization, as indexed by mixed handedness, is associated with mild sub clinical language dysfunction, rather than non-verbal cognitive ability, and this might be relevant to the expression of psychosis phenotype.

Adolescent↗

PubMed2006

The mirror antisaccade task: direction-amplitude interaction and spatial accuracy characteristics.

In this study we examined the performance of human subjects in three oculomotor tasks: a visually guided saccade task (VST), a simple antisaccade task (SAT) and a mirror antisaccade task (MAT). The stimulus presentation was identical for all three tasks, and the differentiation of the tasks was based on the instruction given to the subjects. Subjects were instructed to either look at a visually presented target location (visually triggered saccade task), or to look at the opposite direction of the visually presented target (simple antisaccade task) or finally to look at the mirror location opposite to the location of the visually presented target (mirror antisaccade task). The loading of the simple antisaccade task with the addition of the amplitude requirement did not affect the percentage of directional errors but slowed down the onset of antisaccade execution by 19 ms. The amplitude of the directionally correct antisaccade in the mirror antisaccade task showed a significant distortion of the true mirror target location. This dysmetria followed the same qualitative pattern to that observed for the visually guided saccades, i.e., a near-target hypermetria together with a far-target hypometria, but both these features were exaggerated in the mirror antisaccade task. This distorted amplitude modulation of mirror antisaccade amplitude was completely lost in corrected antisaccades that followed a directional error.

Brain↗

PubMed2005

Effect of COMT Val158Met polymorphism on the Continuous Performance Test, Identical Pairs Version: tuning rather than improving performance.

OBJECTIVE: It has been suggested that variation in catechol O-methyltransferase (COMT) activity associated with variation in COMT Val158Met genotypes may result in enhanced or reduced cognitive performance, depending on whether the phenotype requires cognitive stability or cognitive flexibility. The authors' goal was to determine whether, in confirmation of this prediction, performance on a measure of cognitive stability would be associated with Met loading. METHOD: COMT genotyping was investigated in relation to a measure of reaction time variability on the Continuous Performance Test, Identical Pairs Version, in a large and representative sample of 527 young men (mean age=21 years). RESULTS: Met loading was associated with reduced reaction time variability. CONCLUSIONS: Met genotype loading may confer enhanced "tuning" or greater stability in performance, possibly by stabilizing active neural representations in the prefrontal cortex during tasks involving working memory.

Adult↗

PubMed2004

Parallel processing of spatial and serial order information before moving to a remembered target.

Information storage and retrieval from working memory is limited by the capacity of storage mechanisms and attentional processes. Nevertheless, it has been shown that processing of multiple features can proceed independently in working memory. In this study we investigated how serial order and directional information are processed when executing a movement to a remembered target direction. We compared the performance of 11 healthy subjects in 3 motor working memory tasks, one with a varying spatial memory load, one with a varying serial order memory load, and one in which memory load was varied for both features. We found that the spatial information memory load does not affect the ability to store information about serial order and vice versa. Furthermore, movement response latencies indicated that retrieval of information about both features proceeds simultaneously. These results strongly favor independent, parallel working memory systems for processing space and order information in the motor system.

Adult↗

PubMed2004

Variation in catechol-o-methyltransferase val158 met genotype associated with schizotypy but not cognition: a population study in 543 young men.

BACKGROUND: Increased catechol-O-methyltransferase activity associated with variation in catechol-O-methyltransferase valine158 methionine genotypes may result in reduced dopamine neurotransmission in the prefrontal cortex and thus contribute to the poor performance of frontally mediated cognitive tasks and the occurrence of associated negative symptoms observed in patients with schizophrenia; however, reported associations between catechol-O-methyltransferase valine158 methionine genotypes and measures of cognition have not been consistent. METHODS: Catechol-O-methyltransferase genotyping, measures of schizotypy, cognitive measures of memory and attention, as well as the antisaccade eye movement task, a measure sensitive to prefrontal cortical function, were obtained in a sample of 543 young men representative for that age group (mean age 21 years). RESULTS: None of the cognitive measures was associated with catechol-O-methyltransferase valine158 methionine genotypes; however, there was an effect of high-activity allele loading on schizotypy, in particular the negative and disorganization dimensions. CONCLUSIONS: Previously reported inconsistencies in the relationship between catechol-O-methyltransferase valine158 methionine genotypes and cognition were not resolved; however, catechol-O-methyltransferase genotype may affect expression of negative schizotypy by direct or indirect effects on central dopamine neurotransmitter signaling.

Adult↗

PubMed2004

Attentional facilitation of response is impaired for antisaccades but not for saccades in patients with schizophrenia: implications for cortical dysfunction.

The facilitation of response known as the "gap effect" (a decrease of response latency), observed for saccades and antisaccades when attention is modulated prior to such eye movements, was studied in patients with schizophrenia and in controls. The hypothesis tested was whether patients would show a deficient attentional facilitation in response latency. Fifteen patients with schizophrenia and 17 healthy controls performed blocks of saccades and antisaccades in a "gap" condition and an "overlap" condition. Saccade and antisaccade response latencies as well as the error rate for antisaccades were measured for each subject. A similar gap effect (decrease in latency for the gap compared to the overlap condition) was present in the saccade task for patients and controls. In contrast the gap effect in the antisaccade task was absent in 50% of patients compared to none of the controls. This finding was interpreted as indicative of deficient preprocessing in antisaccade-specific cortical areas in schizophrenia (such as the prefrontal cortex), while visually guided saccade processing remained intact. Our results, in addition to many other recent findings, could lead to specific hypotheses on cortical dysfunction in schizophrenia.

Adult↗

PubMed2004

The effects of increasing memory load on the directional accuracy of pointing movements to remembered targets.

The directional accuracy of pointing arm movements to remembered targets in conditions of increasing memory load was investigated using a modified version of the Sternberg's context-recall memory-scanning task. Series of 2, 3 or 4 targets (chosen randomly from a set of 16 targets around a central starting point in 2D space) were presented sequentially, followed by a cue target randomly selected from the series excluding the last one. The subject had to move to the location of the next target in the series. Correct movements were those that ended closer to the instructed target than any other target in the series while all other movements were considered as serial order errors. Increasing memory load resulted in a large decrease in the directional accuracy or equivalently in the directional information transmitted by the motor system. The constant directional error varied with target direction in a systematic fashion reproducing previous results and suggesting the same systematic distortion of the representation of direction in different memory delay tasks. The constant directional error was not altered by increasing memory load, contradicting our hypothesis that it might reflect a cognitive strategy for better remembering spatial locations in conditions of increasing uncertainty. Increasing memory load resulted in a linear increase of mean response time and variable directional error and a non-linear increase in the percentage of serial order errors. Also the percentage of serial order errors for the last presented target in the series was smaller (recency effect). The difference between serial order and directional spatial accuracy is supported by neurophysiological and functional anatomical evidence of working memory subsystems in the prefrontal cortex.

Adult↗

PubMed2004

Factorial composition of self-rated schizotypal traits among young males undergoing military training.

The aim of this study within the Athens Study of Psychosis Proneness and Incidence of Schizophrenia (ASPIS) was the examination of the latent structure of schizotypal dimensions among a large population of young male conscripts in the Greek Air Force during their first week of military training. Confirmatory factor analysis (CFA) was conducted on 1,355 reliable responders to the self-rated Schizotypal Personality Questionnaire (SPQ), which covers all nine aspects of DSM-III-R schizotypal personality disorder (SPD). A four-factor model (cognitive/perceptual, paranoid, negative, and disorganization schizotypal dimensions) provided a better fit to the data than did other competing models (one-, two-, three-, four, and five-factor models). This result is in agreement with recent findings supporting the notion of a multidimensional construct of the schizotypy and related schizophrenia phenotype.

Adult↗

PubMed2003

Antisaccade performance of 1,273 men: effects of schizotypy, anxiety, and depression.

A total of 1,273 conscripts of the Greek Air Force performed antisaccades and completed self-reporting questionnaires measuring schizotypy and current state-dependent psychopathology. Only 1.0% of variability in antisaccade performance indices was related to psychometric scores in the population and could be attributed more to current state-dependent symptoms such as anxiety rather than to schizotypy. In contrast, a specific increase of error rate and response latency variability and a high correlation of these 2 variables was observed in a group with very high schizotypy scores. This effect was independent of anxiety and depression, suggesting that a specific group of psychosis-prone individuals has a characteristic deviance in antisaccade performance that is not present in the general population.

Adolescent↗

PubMed2003

Single-pulse transcranial magnetic stimulation of parietal and prefrontal areas in a memory delay arm pointing task.

Fifteen healthy volunteers performed a memory-pointing task using their right arm while single-pulse transcranial magnetic stimulation (TMS) above motor threshold was applied over the posterior parietal or prefrontal cortex of the left or right hemisphere in four blocks of trials. The stimulation was randomly delivered at one of three time intervals during the 3-s delay period (early: 300 ms, intermediate: 1,500 ms, late: 2,700 ms). A separate block with no stimulation was used as control. Only early left parietal stimulation resulted in an increase in the variance of movement amplitude but not direction for all targets in two-dimensional space (both hemifields). The results point to the significance of the contralateral posterior parietal cortex early on during the memorization of the target for an upcoming movement. Taking into consideration the limitations of TMS and those imposed by the particular task, the lack of specific effects of prefrontal stimulation provides evidence that these areas might not be involved in the performance of simple memorized arm movements.

Adult↗

PubMed2002

EEG cortical potentials preceding vergence and combined saccade-vergence eye movements.

Previous event-related potential (ERP) studies of eye movements were restricted to saccades, the rapid conjugate movements used to change direction of fixation. Our study explored ERP activity for vergence eye movements used for the adjustment of the angle of the visual axes to the distance of the object. These movements are essential when exploring the natural 3D world. Subjects made the following visually guided movements to LED targets: pure convergence or divergence along the median plane, pure lateral saccades within the same distance, and combined movements (lateral and divergent or convergent). ERPs were recorded from 14 surface electrodes and were analyzed for 200 ms prior to the onset of the eye movement. The highest activation was observed prior to vergence. Activation was diffused and peaked at 50 ms prior to the onset of vergence. Combined vergence and sacccadic movements revealed a composite pattern of ERP activity from both saccades and pure vergence. These findings suggest a cortical substrate for vergence eye movements in humans that is engaged in the natural exploration of visual space.

Adult↗