Biomedical subjects

Nicolas Georgieff

Publications and source records attributed to Nicolas Georgieff.

8 recordsLinked to original sources

PubMed2006

Goal-directed action representation in autism.

The aim of the present study was to investigate the ability of individuals with autism to represent goal-directed behavioural actions. We compared the performance of subjects with autism (n=16), mentally retarded subjects (n=14) and normal healthy subjects (n=15) in a sequencing task consisted in arranging pictures of single events in their appropriate order so as to make coherent stories. Three types of actions were presented: (a) actions on objects; (b) actions on objects in a broader spatio-temporal context; (c) interactive actions. Autistic subjects were impaired in arranging sequences of actions on objects, as compared to both control groups. This impairment might contribute to explaining both executive deficits and difficulties in understanding others' behaviour in autism.

Adolescent↗

PubMed2005

Impairment in event sequencing in disorganised and non-disorganised patients with schizophrenia.

It has been suggested that thought disorder in schizophrenia is associated with impaired executive functions and with a defective understanding of others' behaviour. Action sequence knowledge processing and goal detection are considered as crucial components of executive functioning. Here, we used a picture-sequencing task to assess the ability of schizophrenic patients (n = 40) with and without disorganisation symptoms to arrange different types of action sequence representations. Disorganisation symptoms appear to be associated with a general sequencing impairment, while patients without disorganisation symptoms displayed difficulties in ordering sequences requiring subjects to infer mental states in story characters along with a relatively preserved performance in correctly arranging mechanical or behavioural event sequences. These results reveal that only schizophrenic patients without disorganisation symptoms show a selective deficit in mentalising abilities whereas disorganisation symptoms are associated with a more severe event sequencing impairment probably reflecting basic failures of inferential reasoning.

Adult↗

PubMed2005

Mental rotation in schizophrenia.

Motor imagery provides a direct insight into action representations. The aim of the present study was to investigate the level of impairment of action monitoring in schizophrenia by evaluating the performance of schizophrenic patients on mental rotation tasks. We raised the following questions: (1) Are schizophrenic patients impaired in motor imagery both at the explicit and at the implicit level? (2) Are body parts more difficult for them to mentally rotate than objects? (3) Is there any link between the performance and the hallucinating symptom profile? The schizophrenic patients (n = 13) displayed the same pattern of performance as the control subjects (n = 13). More particularly, schizophrenic patients' reaction time varied as a function of the angular disparity of the stimuli. On the other hand, they were significantly slower and less accurate. Interestingly, patients suffering from hallucinations made significantly more errors than non-hallucinatory patients. We discussed these latter results in terms of deficit of the forward model. We emphasized the necessity to distinguish different levels of action, more or less impaired in schizophrenia.

Adult↗

PubMed2005

Event-related potentials during rule processing in schizophrenia.

Several studies have shown that schizophrenia is characterized by impaired frontal lobe functions, functions that are responsible, for example, for the management of rules, strategic reasoning, and selective attention. Using event-related potentials (ERP), we assessed the brain's electrical activity in a group of patients with schizophrenia (n=11) and a healthy control group (n=14) during a reaction time task requiring the use of a rule. ERP waves were compared with those elicited in a similar task based on a direct sensory association. In the control group, ERP analyses showed a negative wave moving from the posterior to the anterior regions of the scalp in a latency range of 250-400 ms. Then, the negativity remained at the frontal scalp region in a latency range of 400-800 ms. In this group, the amplitude was higher during the rule operation than during the sensory association task. In schizophrenic patients, the anteroposterior component of the negative wave was totally absent in both tasks, and we did not find a modulation of the ERP by the task. Frontal scalp negativity was observed, but its latency was longer and its amplitude lower than in the control group. We discuss these findings in terms of the frontoposterior disconnection hypothesis.

Adult↗

PubMed2004

Neural correlates of action attribution in schizophrenia.

Patients with first-rank symptoms (FRS) of schizophrenia do not experience all of their actions and personal states as their own. FRS may be associated with an impaired ability to correctly attribute an action to its origin. In the present study, we examined regional cerebral blood flow (rCBF) with positron emission tomography during an action-attribution task in a group of patients with FRS. We used a device previously used with healthy subjects that allows the experimenter to modulate the subject's degree of movement control (and thus action attribution) of a virtual hand presented on a screen. In healthy subjects, the activity of the right angular gyrus and the insula cortex appeared to be modulated by the subject's degree of movement control of the virtual hand. In the present study, the schizophrenic patients did not show this pattern. We found an aberrant relationship between the subject's degree of control of the movements and rCBF in the right angular gyrus and no modulation in the insular cortex. The implications of these results for understanding pathological conditions such as schizophrenia are discussed.

Adult↗

PubMed2004

Increased perception of loudness in autism.

Clinical reports on autism describe abnormal responses to auditory stimuli such as intolerance to sounds. The present study assessed subjective perception of loudness in subjects with autism compared to healthy controls, using two psychoacoustic tests. First, the auditory dynamic range was evaluated at six different tone frequencies. Secondly, loudness growth as a function of the intensity level of a 1 kHz tone was estimated. Verbal responses from a group of 11 children and adolescents with autism were compared to responses of 11 age- and gender- matched healthy controls. Smaller auditory dynamic ranges were found in the autistic group than in the control group, as well as increased perception of loudness, indicating hyperacusis in subjects with autism.

Acoustic Stimulation↗

PubMed2002

Gaze direction determination in schizophrenia.

It has been proposed that an impairment in gaze determination is responsible for the paranoid symptoms reported in schizophrenia. To address this, we examined the gaze discrimination system in schizophrenia. Thirty-two patients suffering from schizophrenia (20 patients with persecutory delusions and 12 patients without such delusions) were compared to 32 control subjects on two specific tasks. In the first task, the subjects had to determine whether 130 portraits were looking right or left. In the second task the subjects were asked to determine whether or not 130 portraits were looking at them. The absolute threshold of difference used to investigate the influence of instruction on gaze discrimination did not show any difference between patients with schizophrenia, whatever paranoid or not, and control subjects. Paranoid patients, as well as controls, displayed a significantly finer discrimination threshold in the right vs. left judgment than in the self vs. non-self judgment. Subjects with schizophrenia were able to discriminate gaze direction in the two tasks, but they took significantly more time in the task requiring to determine the presence or the absence of a mutual gaze contact than in the other one, whereas controls took the same duration to elicit both tasks. These data are consistent with those reporting that perceptual abilities are spared in schizophrenia while delusions are related to an impairment of a higher level of analysis.

Adult↗

PubMed2002

[Neurodevelopmental hypothesis of schizophrenia].

Re-assembling the heterogeneic arguments in favour of organic factors (be whether genetic or early environmental exposures), the neuro-developmental hypothesis of schizophrenia proposes that the illness is due to an early insult (pre- or perinatal) that affects the development of the brain, leading to anomalies that express themselves only after the event, once cerebral maturity has been attained. The hypothesis rests on three types of arguments; neuropathological, clinical and epidemiological. We will successively examine the neuropathological observations made in post-mortem studies of the brains of affected patients and the studies in morphological neuro-imagery, then the results of research into aetiological factors, and the data concerning children susceptible to later development of the illness. Finally, we will address the mechanisms proposed to explain why the illness only presents, on average, 20 years after the initial hypothetical insult.

Adolescent↗