Bernard Claverie

Verbal fluency output in children aged 7-16 as a function of the production criterion: Qualitative analysis of clustering, switching processes, and semantic network exploitation

Developmental changes in childrens verbal fluency were explored in this study. One hundred and forty children aged from 7 to 16 completed four verbal fluency tasks, each with a different the production criterion (letter, sound, semantic, and free). The age differences were analyzed both in terms of number of words produced, and clustering, switching, and semantic network exploration. Analysis of the number of words produced showed a larger difference between the 7-8- and the 9-10-year-olds in semantic than in letter fluency, but this difference gradually disappeared with increasing age for semantic fluency while remaining constant for letter fluency. In letter fluency production, age modified both the number of switches and clusters formed whereas in semantic fluency tasks, only cluster size changed with age. Concerning the semantic network exploration indicators derived from the supermarket fluency task, the number of categories sampled increased from 11 to 12 years, but efficient semantic exploitation occurred only after the age of 13-14 years. These results are discussed in terms of the development of strategic retrieval components and categorical knowledge.

Short- and Long-Delay Intracranial ERP Repetition Effects Dissociate Memory Systems in the Human Brain

Prior exposure to a stimulus can facilitate the performance to subsequent presentations of that stimulus. ERP studies have shown that this facilitation is associated with the modulation of two components (N400 and P600). Investigation of the time course of both behavioral and ERP repetition effects have led to the assumption that it is subserved by the combination of at least two mechanisms operating at different time-points: a short-delay semantic activation and a long-lasting episodic mechanism. The present experiment recorded intracranial ERPs from various structures during a continuous recognition memory task to investigate the respective contribution of the different brain regions to short-and long-delay ERP repetition effects. The results are in good agreement with both the classical neuropsychological literature and the more recent data obtained with functional imagery techniques. They provide electrophysiological evidence of multiple anatomo-functional memory systems in the human brain: a short-term semantic activation system and a long-term episodic memory system, with interface structures that coordinate the functioning of these two systems.

Effect of age of onset of temporal lobe epilepsy on the severity and the nature of preoperative memory deficits.

The nature and severity of pre-operative memory deficits observed in unilateral temporal lobe epilepsy depend upon a number of variables. Among these variables, age of seizure onset seems to be important. The age at which the lesion is sustained could modify the normal functional organization of the brain. Many studies have examined the effect of age of onset on the severity of memory deficits but have seldom focused on the nature of such deficits (verbal/nonverbal) as a function of epileptic focus laterality. This study investigates the effect of age of onset on the nature and severity of memory impairments. Fifty-six epileptics with unilateral temporal lobe epilepsy and 20 normal subjects were administered a neuropsychological evaluation. Four groups of patients were constituted: left or right temporal lobe epilepsy with early (0-5 years) or late (10 years and over) age of seizure onset. The early group showed major verbal and nonverbal memory deficits. The late group presented minor specific deficits: essentially verbal deficits with left temporal lobe seizures and nonverbal deficits with right temporal lobe seizures. These results may be interpreted in the framework of ontogenesis theories of hemispheric specialization.

Exploration of hemispheric specialization and lexico-semantic processing in unilateral temporal lobe epilepsy with verbal fluency tasks

Verbal production has been shown to rely on both hemispheres differentially. To determine how lateralized brain lesions affect the generation of isolated words, we evaluated three subject groups: normal controls (n=22), and patients with right (n=23), and left (n=22) non-operated temporal lobe epilepsy (TLE) using three verbal fluency tasks (letter, phonetic, semantic). LTLE patients produced fewer words than controls in the phonetic, letter, semantic conditions, whereas RTLE patients were only impaired in the semantic task. Hence, there would be a hemispheric specialization in language where phonetic processing involves mostly the left temporal lobe and semantic aspects of production involve both temporal lobes. And, in order to study disruption of semantic lexicon involved in supermarket fluency (to name things which can be bought in a supermarket), specific indicators Tröster et al., (1998) [Tröster AI, Fields JA, Testa JA, Paul RH, Blanco CR, Hames KA, Salmon DP, Beatty WW. Cortical and subcortical influences on clustering and switching in the performance of verbal fluency Tasks, Neuropsychologia 1998;36:295-304.] were exploited. Our results indicated that TLE groups made fewer category shifts than controls. Also, RTLE patients used labels more frequently and produced fewer exemplars. Results show the specificity of processing according to cue, and suggest that the semantic fluency deficits due to TLE be primarily due to an alteration of the mental lexicon.

Multiple subpial transection: report of 7 cases

7 cases of pure multiple subpial transection (MST) without associated cortical resection, for treatment of pharmaco-resistant partial epilepsy localized in highly functional cortical area, are reported. The transections were performed following the technique described by Morrell. The follow-up period ranged from 1 to 4 years. MST induced no significant neurological handicap: only 2 patients experiencing a transitory sensory-motor deficit and with total recovery within 1 month. With respect to seizures, 5 patients were improved with a decrease in seizure frequency of 100, 95, 75, 60 and 40%, respectively. Complex partial seizures changed postoperatively into simple partial seizures in 1 case. In conclusion, this procedure seems to be adequate, although no statistically significant results are available at this time. In our series, we believe failures could be attributed to either a very restricted area of transection or to an incorrect delimitation of the epileptic focus.

Verbal memory compensation: application to left and right temporal lobe epileptic patients.

This study investigates the compensatory impact of cognitive aids on left and right temporal lobe epileptic patients suffering from verbal memory disorders, who were candidates for surgery. Cognitive aids are defined in the levels-of-processing framework and deal with the depth of encoding, the elaboration of information, and the use of retrieval cues. Results indicate differential compensatory impact for left and right epileptic patients and are discussed according to the HERA model and the compensation framework.

Time Course of Cognitive Recovery After Propofol Anaesthesia: A Level of Processing Approach

The aim of this study was to investigate the time course of recovery of verbal memory after general anaesthesia, as a function of the level (shallow or deep) of processing induced at the time of encoding. Thirty-one patients anaesthetized with propofol and alfentanil were compared with 28 control patients receiving only alfentanil. Memory functions were assessed the day before and 1, 6 and 24 hr after operation. Results show that for the anaesthetized group, shallow processing was impaired for 6 hr after surgery whereas the deeper processing was not recovered even at 24 hr. In addition, no specific effect of age was found.

Age effect in recall performance according to the levels of processing, elaboration, and retrieval cues

The present study was conducted to investigate the incidence of several factors contributing to age-related memory decrement. Variables manipulated include quality (level of processing encoding conditions), the degree of effort and encoding quantitative elaboration (active/passive encoding conditions), and the influence of retrieval support (free-/cued recall conditions). In support of the environmental support hypothesis, middle-old and old subjects benefited more than young ones from cued recall in all the memory tests. Moreover, the results showed a differential (qualitative vs. quantitative) impairment of conceptual processing between the middle-old and the old-age groups. In the middle-olds, age differences were abolished by deep processing in old adults, age differences were attentuated only with deep and active processing associated with retrieval support. These gradual memory impairments are evaluated according to Mandlers model of memory (1979, In L. G. Nilsson\[Ed.], Perspective in memory research. Hillsdale: Lawrence-Erlbaum), and the environmental support hypothesis is discussed in terms of the involvement of encoding and retrieval operations required by the memory task.The present study was conducted to investigate the incidence of several factors contributing to age-related memory decrement. Variables manipulated include quality (level of processing encoding conditions), the degree of effort and encoding quantitative elaboration (active/passive encoding conditions), and the influence of retrieval support (free-/cued recall conditions). In support of the environmental support hypothesis, middle-old and old subjects benefited more than young ones from cued recall in all the memory tests. Moreover, the results showed a differential (qualitative vs. quantitative) impairment of conceptual processing between the middle-old and the old-age groups. In the middle-olds, age differences were abolished by deep processing in old adults, age differences were attentuated only with deep and active processing associated with retrieval support. These gradual memory impairments are evaluated according to Mandlers model of memory (1979, In L. G. Nilsson [Ed.], Perspective in memory research. Hillsdale: Lawrence-Erlbaum), and the environmental support hypothesis is discussed in terms of the involvement of encoding and retrieval operations required by the memory task.

Functional heterogeneity of the frontal lobe: evidence from intracranial memory ERPs

Intracranial event-related potentials (ERPs) elicited during a recognition memory task were recorded in 17 epileptic patients by using depth electrodes sampling different regions within the frontal lobe. The task was a continuous recognition memory task in which repeated items were presented after six or 19 intervening items following their first presentation. Such a paradigm is one of the experimental tasks requiring both short-term memory and interference control processes which are thought to be subserved by the frontal lobe. The results provide electrophysiological support for the classical view that the frontal lobe is heterogeneous region encompassing a number of functional systems subserving different aspects of memory processing. The anterior dorsolateral and cingulate cortices were found to contribute to short-term memory and recency judgment. The orbital region is more likely to be involved in interference control. The posterior part of the frontal cortex plays a role in some processes related to the control of the motor response.

Location of the Epileptic Zone and Its Physiopathological Effects on Memory-Related Activity of the Temporal Lobe Structures: A Study with Intracranial Event-Related Potentials

Summary: Purpose: Neuropsychological research with epileptic patients has suggested that the location of seizure focus may be an important variable determining the nature and severity of memory impairments. According to this assumption, this study was designed to investigate the effects of the location of the epileptic zone on the memory‐related activity recorded directly from different temporal lobe structures.