Biomedical subjects

Laurent Pezard

Publications and source records attributed to Laurent Pezard.

5 recordsLinked to original sources

PubMed2006

Distinct patterns of striatal medium spiny neuron activity during the natural sleep-wake cycle.

Striatal medium-sized spiny neurons (MSNs) integrate and convey information from the cerebral cortex to the output nuclei of the basal ganglia. Intracellular recordings from anesthetized animals show that MSNs undergo spontaneous transitions between hyperpolarized and depolarized states. State transitions, regarded as necessary for eliciting action potential firing in MSNs, are thought to control basal ganglia function by shaping striatal output. Here, we use an anesthetic-free rat preparation to show that the intracellular activity of MSNs is not stereotyped and depends critically on vigilance state. During slow-wave sleep, much as during anesthesia, MSNs displayed rhythmic step-like membrane potential shifts, correlated with cortical field potentials. However, wakefulness was associated with a completely different pattern of temporally disorganized depolarizing synaptic events of variable amplitude. Transitions from slow-wave sleep to wakefulness converted striatal discharge from a cyclic brisk firing to an irregular pattern of action potentials. These findings illuminate different capabilities of information processing in basal ganglia networks, suggesting in particular that a novel style of striatal computation is associated with the waking state.

Action Potentials↗

PubMed2006

Autobiographical memory deficit in anorexia nervosa: emotion regulation and effect of duration of illness.

Emotional deficits in anorexia nervosa can be expressed in autobiographical memory recall. The aim of this study is to test whether deficits in autobiographical memory exist in anorexic patients and concern specifically negative or positive emotional valence. Moreover, it is unclear whether these deficits are dependent upon comorbid aspects (depression, alexithymia, and anxiety) or upon illness duration. Anorexic patients (n=25) were compared to healthy volunteers based on their clinical assessment, explicit memory test score, and autobiographical memory test score. The study makes use of the autobiographical test of Williams and Scott, which involves specific emotional cues to elicit memory. Anorexic patients recalled more general memories than controls in autobiographical memory test, but had no deficit in explicit memory test. This pattern, observed both for negative and positive cues, was neither related to depression or alexithymia, nor to anxiety severity, but increased significantly with illness duration. These results show that anorexic patients are characterized by relative difficulty in the integration of both negative and positive emotional experiences, and that this impairment is reinforced by illness duration.

Adult↗

PubMed2005

Neuroleptic-induced catalepsy: electrophysiological mechanisms of functional recovery induced by high-frequency stimulation of the subthalamic nucleus.

High-frequency stimulation (HFS) of the subthalamic nucleus (STN) remarkably alleviates motor disorders in parkinsonian patients. The mechanisms by which STN HFS exerts its beneficial effects were investigated in anesthetized rats, using a model of acute interruption of dopaminergic transmission. Combined systemic injections of SCH-23390 [R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5,-tetrahydro-1H-3-benzazepine] and raclopride, antagonists of the D1 and D2 classes of dopaminergic receptors, respectively, were performed, and the parameters of STN HFS that reversed the neuroleptic-induced catalepsy were determined in freely moving animals. The effects of neuroleptics and the impact of STN HFS applied at parameters alleviating neuroleptic-induced catalepsy were analyzed in the substantia nigra pars reticulata (SNR), a major basal ganglia output structure, by recording the neuronal firing pattern and the responses evoked by cortical stimulation. Neuroleptic injection altered the tonic and regular mode of discharge of SNR neurons, most of them becoming irregular with bursts of spikes and pauses. The inhibitory component of the cortically evoked response, which is attributable to the activation of the direct striatonigral circuit, was decreased, whereas the late excitatory response resulting from the indirect striato-pallido-subthalamo-nigral circuit was reinforced. During STN HFS, the spontaneous firing of SNR cells was either increased or decreased with a global enhancement of the firing rate in the overall population of SNR cells recorded. However, in all of the cases, SNR firing pattern was regularized, and the bias between the trans-striatal and trans-subthalamic circuits was reversed. By these effects, STN HFS restores the functional properties of the circuits by which basal ganglia contribute to motor activity.

Action Potentials↗

PubMed2005

Dynamical quantification of schizophrenic speech.

Schizophrenic speech has been studied both at the clinical and linguistic level. Nevertheless, the statistical methods used in these studies do not specifically take into account the dynamical aspects of language. In the present study, we quantify the dynamical properties of linguistic production in schizophrenic and control subjects. Subjects' recall of a short story was encoded according to the succession of macro- and micro-propositions, and symbolic dynamical methods were used to analyze these data. Our results show the presence of a significant temporal organization in subjects' speech. Taking this structure into account, we show that schizophrenics connect micro-propositions significantly more often than controls. This impairment in accessing language at the highest level supports the hypothesis of a deficit in maintaining a discourse plan in schizophrenia.

Adult↗

PubMedDate not supplied

Autobiographical memory in major depression: a comparison between first-episode and recurrent patients.

Autobiographical memory in depression is characterized by an increase in general memory evocation. The aim of this study is to compare autobiographical memory in patients with a first depressive episode and in recurrent patients before and after recovery, using Williams' and Scott's autobiographical memory test. Our results show an increase of the number of general memories only with positive cue words in both groups of patients during the depressive episode. After clinical improvement, this specificity remains in recurrent patients who, in addition, recall more general memories for negative words. By contrast, patients with a first depressive episode are no longer different from controls. These results show both an overgeneralization and a deficit in positive memory access during the depressive episode, whatever the number of previous episodes. Moreover, recurrence chronically modifies access to emotional memories.

Adult↗