Biomedical subjects

Nicolas Franck

Publications and source records attributed to Nicolas Franck.

26 records · Page 2Linked to original sources

PubMed2003

Augmentation of induced visual gamma activity by increased task complexity.

Recently the study of induced gamma band oscillations has focused on their modulation by top-down processes, mainly attention. Numerous studies have observed an increase in induced gamma band energy with increases in covert selective attention and visual perception. The current study investigated the modulation of visually induced gamma band oscillations by top-down processes associated with task complexity. Fourteen human subjects performed a reaction time task under two experimental conditions that differed in task complexity. In one, subjects simply had to press one of four buttons that corresponded to a colour stimulus shown to the subject. In the second, the stimulus response mapping was altered by the implementation of a rule, thus increasing task complexity. Cortical electrical activity was recorded using a 65 electrode whole scalp electroencephalographic (EEG) net. The EEG activity was analysed using Morlet wavelets to produce time-frequency maps. Although induced gamma band activity was observed in both conditions, there was significantly greater energy during the rule-operation condition at approximately 276 ms after the appearance of the stimulus. This increase was localized to electrodes overlying the right-central parietal scalp. The results of this study show that top-down processes modulate the level of induced gamma band activity. We discuss these findings in terms of the role of gamma oscillations in the construction of a sensory representation useful for a correct motor response.

Adolescent↗

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↗

PubMed2002

Use and automation of a rule in schizophrenia.

Schizophrenia is associated with cognitive deficits and information-processing anomalies. Several studies have shown impairments in frontal lobe functions such as discovering rules, adopting strategies and working memory. We have evaluated the performances of schizophrenic patients on three different tasks of information processing. The first was a simple reaction time task, the second consisted of discriminating the color of the stimuli, and the third required the use of a rule of permutation. The schizophrenic patients (n=17) showed a task-dependent increase in time for responses in comparison with the control group (n=17). This increase was particularly important in the last task, which requires the use of the rule. These results confirm and expand the previously described impairment of patients with schizophrenia in the ability to use rules. They are discussed in terms of deficit in executive functions probably due to frontal lobe malfunctioning.

Adult↗

PubMed2002

Selective attention to facial emotion and identity in schizophrenia.

The selective attention to facial emotion and identity was investigated in 12 patients with schizophrenia and 12 healthy participants. Both patients and controls were required to perform two classification tasks (according either to identity or emotion). Two separate values for identity (person A/person B) and for emotion (fear/anger) were used. When the classification task was on one dimension, the other dimension was either correlated, constant, or orthogonal (Garner WR. The Processing of Information and Structure. Potomac, MD: Erlbaum, 1974, Garner WR. Interaction of stimulus dimensions in concept and choice processes. Cognitive Psychology 1976;8:98-123). Results indicated that both patients and healthy participants had an asymmetrical pattern of performance: they were able to selectively attend to the identity of the face presented, regardless of the emotion expressed on the face, but variation in identity interfered with the classification of facial emotion. Moreover, a correlational study indicated that the identity interference on emotion classification for schizophrenic patients covaried with the severity of their negative symptoms. The selective attention competencies in schizophrenia and the independence hypothesis of emotion and face recognition are discussed in the framework of current face recognition models.

Adult↗

PubMed2002

Perception of self-generated action in schizophrenia.

INTRODUCTION: Self-generated actions involve central processes of sensorimotor integration that continuously monitor sensory inputs to ensure that motor outputs are congruent with our intentions. This mechanism works automatically in normal conditions but becomes conscious whenever a mismatch happens during the execution of action between expected and current sensorimotor reafferences. It is now admitted in the literature that sensorimotor processes as well as the ability to predict the consequences of our own actions imply the existence of a forward model of action, which is based on efference copies. Recently, it has been proposed that positive symptoms expressed by schizophrenic patients, such as delusions of control or thought insertions, arise because of a deficiency in this forward model, and more particularly, because of a lack of awareness of certain aspects of motor control derived from such an internal model. METHOD: To test further this hypothesis, 19 schizophrenic patients (10 with and 9 without Schneiderian symptoms) and 19 control subjects performed a visuo-motor conflict task and had verbally to report the felt position of their hand at the end of each trial. RESULTS: Under this experimental procedure, schizophrenic patients--whatever their clinical phenotype--failed to switch to a conscious representation of their hand movements, and then consequently to maintain their level of performance for the sensorimotor adjustment in comparison with controls. CONCLUSION: Our findings suggest two facts. First, that a functional monitoring of action, based on a forward.

Journal Article↗

PubMed2002

Cerebral blood flow changes associated with Schneiderian first-rank symptoms in schizophrenia.

The authors examined the severity of Schneiderian first-rank symptoms in relation to regional cerebral blood flow (rCBF) with the use of PET. Eighty-seven schizophrenic patients were imaged during an eyes-closed condition during which they were instructed to relax and not perform any specific task (random episodic silent thought, or REST). Schneiderian symptoms were rated by using structured assessment instruments. The Schneiderian score of the patients was positively correlated with rCBF in right superior parietal cortex and negatively correlated with rCBF in left posterior cingulate gyrus and in left lingual gyrus. The results of this study demonstrate a cerebral pattern of activation related to Schneiderian symptoms and reinforce the hypothesis of an involvement of cortical areas that mediate space and body representation in such phenomena.

Adult↗

PubMed2002

Reduced P300 amplitude in a visual recognition task in patients with schizophrenia.

We studied top-down visual processes in schizophrenia by analyzing visual event-related potentials (ERPs) during a gestalt recognition task, after subjects (patients with schizophrenia, n = 10; controls, n = 14) were trained to perceive three different geometrical shapes. Recognition performance of patients was poorer under both the figure and the nonfigure conditions then that of normal controls. ERPs analysis indicated that P300 amplitudes of the patients were significantly smaller than those of controls during correct figure detection trials. Moreover, topographical analysis of the differences in ERPs during the figure vs the nonfigure condition showed an earlier, more positive and more widely distributed P300 in controls than in patients with schizophrenia. Our study supports the misconnection hypothesis of schizophrenia and highlights the difficulty of the patients to refer to previous experience in order to filter incoming information. In a visual recognition task, this misconnection syndrome might induce a failure to integrate information stored in the frontal and prefrontal sites with incoming stimuli.

Adult↗