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 children's 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.

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.

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 Mandler's 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.

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.

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.

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. METHODS: Intracranial event-related potentials (ERPs) were recorded during a continuous recognition memory task, which is known to elicit the modulation of N400 and P600 components (i.e., the ERP old/new effect). The patients were separated into three groups according to the location of their epileptic zone: unilateral temporal (UTE), temporal plus extratemporal (TEE), and bitemporal (BTE). Recordings were obtained from three temporal lobe structures: hippocampus, amygdala, and lateral temporal cortex. RESULTS: The results showed that in the hippocampus, the ERP old/new effect was abolished in the TEE group only. In the amygdala, although largely unaffected, the ERP modulation appeared to be more impaired in UTE patients. Contrasting with these data is the observation that the magnitude and reliability of the ERP old/new effect recorded at the neocortical level increases as the epileptic zone extends to the temporal lobes (i.e., BTE>TEE>UTE). CONCLUSIONS: It is concluded that the memory-related activity modulation of memory ERPs recorded from different temporal lobe structures is affected differently by the presence of an epileptic zone as a function of its location. The possible clinical implications of these findings in surgery planning are also discussed.

Callosotomy for intractable epilepsy: overall outcome.

The effectiveness of callosotomy to the control of medically intractable epilepsy is still discussed fifty years after the first reported cases. Nevertheless patient selection, type of seizures and epileptic syndromes are now better determined. Atonic and tonic astatic seizures characterized both by clinical and electroencephalographical specific patterns, are the most responsive. A favorable outcome, from > 50% reduction in seizure frequency to a complete cessation, is obtained from 60 to 80% of the patients. For tonic-clonic seizures, favorable outcome fluctuates from 40% to 80% principally according to the extension of the section. Other types of seizures are not indicated for callosotomy even though some improvement may be observed. Symptomatic secondary generalized epilepsy with predominent unilateral lesion and epileptic focus on bifrontal lobe epilepsy are the most suitable indication. True generalized epilepsies are associated with a less favorable outcome. Indeed, axial spasms, the most frequent type of drop attacks in the Lennox-Gastaut syndrome, probably do not have a cortical origin. Quality of life and social adjustment are assessed from a cohort of 20 cases of anterior two-third callosotomy. Actual benefits are in close connection with both seizure relief and age at operation. To obtain a gain in social independence not only seizure control has to be better but also surgery must be performed sooner.

Differential involvement of the human temporal lobe structures in short- and long-term memory processes assessed by intracranial ERPs.

Intracranial event-related potentials (ERPs) elicited during a recognition memory task were recorded in 25 epileptic patients by using depth electrodes sampling four different regions within the temporal lobe (amygdala, hippocampus, anterior and posterior temporal cortices). The task was a continuous recognition memory task in which repeated items were presented after 6 or 19 intervening items following their first presentation. This study was performed to investigate the respective role of the different temporal lobe structures in short-term memory (STM) and long-term memory (LTM) processing. Subregions of the temporal lobe were differently involved in these two memory systems. The posterior temporal cortex is specifically involved in STM processing, whereas the amygdala, hippocampus, and anterior temporal cortex contribute to both STM and LTM. Moreover, it appeared that the latter structures play their own role in LTM. The anterior temporal cortex and amygdala may contribute to recency discrimination, and the hippocampus seems rather to be involved in maintaining memory traces. These findings suggest that the temporal lobe structures may function in a complementary way by subserving different aspects of information processing.

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.

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.

Effects of temporal versus temporal plus extra-temporal lobe epilepsies on hippocampal ERPs: physiopathological implications for recognition memory studies in humans.

The present experiment was designed to investigate the incidence of temporal and extra-temporal epileptogenic lesions on hippocampal activity related to recognition memory. Hippocampal event-related potentials (ERPs) were recorded during a recognition memory task for pictures in patients with unilateral temporal lobe epilepsy and in patients with combined temporal and extra-temporal (frontal or parietal) epileptogenic foci. In the first group, the comparison between correctly recognized pictures and new distractors revealed that the usual ERP (N400/P600) 'old/new' effects were not dramatically affected by the presence of a temporal epileptogenic lesion. In contrast, these effects were absent in multifocal epilepsy patients, indicating that frontal and parietal brain regions play a part in the modulation of hippocampal ERP and related memory processing. These results suggest that ERP 'old/new' effects are dependent on interactions between frontal, parietal and medial temporal structures. Together with the results of other recent studies devoted to locating the neural sources of N400 and P600, the present findings provide physiopathological evidence that ERP 'old/new' effects are subtended by distributed yet interconnected brain regions that are known to play an important role in recognition memory processing.

Intracranial topography of event-related potentials (N400/P600) elicited during a continuous recognition memory task.

To isolate the anatomical locus of the neural activity most important for generating or modulating the scalp-recorded N400 and P600 components elicited during continuous recognition memory tasks, intracranial event-related potentials (ERPs) were recorded from medial and lateral aspects of the temporal, frontal, parietal, and occipital lobes in 25 patients undergoing stereoelectroencephalography for seizure localization. Large-amplitude and polarity-inverted ERPs were recorded from various temporal, frontal, and parietal structures, whereas the memory-related ERP modulation assessed by the ERP repetition effect was present only in those brain areas that play the most important role in memory processing. These data suggest that the scalp-recorded N400 and P600 components may represent the most readily observable aspect of synchronous activity occurring across widely distributed brain structures and neural systems underlying different cognitive mechanisms, which all contribute to some aspect of information processing during recognition memory.

[Social outcome of 20 anterior callosotomies for drug-resistant epilepsy]. / Devenir social de 20 callosotomies antérieures pour épilepsie pharmacorésistante.

Results of 20 anterior callosotomies with regard to quality of life and social outcome were analysed according to seizure control. Data arise from a retrospective study with the medico-social teams. Drop attacks with tonic or atonic seizures decreased in 11 cases. Nevertheless only 8 cases (40%) have experienced a reduction of more than 70% in seizure frequency. Neurocognitive status slightly worsened in 3 cases. Age at intervention and type of epileptic syndrome were not predictors of seizure outcome. A subjective improvement in quality of life was reported in 10 cases. A significant improvement in social adjustment was obtained in 7 cases (35%). There was a close correlation between life comfort improvement and reduction in drop attack frequency. Not only seizure control has to be better but also surgery must be performed sooner to obtain a gain in social independence. Finally, successful outcome should be considered as limited. Nevertheless results may be considered taking into account the high severity of the condition and the low morbidity of anterior callosotomy.

A longitudinal assessment of seizure outcome and overall benefit from 100 cortectomies for epilepsy.

Results of 100 cortical resections for 76 temporal, 23 frontal and one parietal lobe epilepsies were studied in terms of seizure relief and overall benefit. A non-homogenous Markov chain model was used to take into account both the intravariability of post-surgical outcome and the differences in duration of follow-up in a group of patients consecutively operated. The seizure free (SF) state was defined as no seizure in the previous five months at first follow up visit and none in the preceding 12 months at subsequent annual visits. For the whole of the population the SF probability was 82%, 66%, 61%, and 62% at six months, one year, two and five years respectively. A better outcome was found for temporal lobe epilepsy (SF probability: 68% at the fifth postoperative year) than for frontal lobe epilepsy (SF probability: 42% at the fifth postoperative year) with a statistically significant difference. Pre- and postoperative interictal signs and symptoms were classified according to their clinical significance: (a) mild handicap--symptoms recognisable but no interference with usual life, and (b) moderate or severe handicap--interference with some or all daily activities. The interictal state was considered more impaired after surgery than before in two situations: (a) either symptoms, absent before surgery, appeared in the postoperative period involving a moderate or severe handicap, or (b) symptoms present before surgery and answerable for a mild or moderate handicap that increased to involve a moderate or severe handicap respectively in the postoperative period. Surgery was considered a major benefit when two conditions were fulfilled-namely, a SF state and no deterioration of the interictal stage when compared with the preoperative period. The probability of obtaining such a benefit was 58%, 51%, 48% and 56% at six months, one year, two and five years respectively. The results suggest that surgery is an effective treatment for more than 50% of long lasting medically intractable epilepsies.

[P3on and P3off in a passive visual protocol]. / P3on et P3off dans un protocole visuel passif.

This study shows the possibility of obtaining visual event-related potentials without active discrimination instructions. The components are similar to the P3 components obtained in classic active protocol. The (P3off) of simple images indicates an interpretation in terms of information processing and change in mental state.

[Slow hippocampal potentials (200-600 ms) and short-term recognition of images in humans: study of the effect of context]. / Potentiels lents (200-600 ms) hippocampiques en reconnaissance à court terme d'images chez l'homme: étude de l'effet de contexte.

The activity of the hippocampic structures recorded during a semantic picture recognition task (Signoret's test) is modified by physical contextual changes. This contextual effect seems to be supported by the left hippocampus.

[Cerebral psychophysiologic study of the processes brought into action by physical context modifications in the short-term recognition of images]. / Etude psychophysiologique cérébrale des processus mis en jeu par les modifications contextuelles physiques en reconnaissance à court terme d'images.

The study of P300 waves and reaction times during the acquisition and recognition of simple symbolic pictures (Signoret's test) shows the extent of "contextual effect" in visual short-term recognition. These results support the "encodage spécifique" theory according to which contextual changes between acquisition and restitution reduce memory efficiency.

[P 300 wave and additive or self-terminated processes in short-term image recognition]. / Onde P 300 et processus exhaustifs ou autoterminés en reconnaissance à court terme d'images.

The study of the P 300 wave during the acquisition and the recognition of simple symbolic pictures shows a self-terminated treatment in short-term visual recognition processes. The results of this study plead in favour of a general principle of psychobiological economy and of a decrease of the mental charge. This principle is at variance with one of the postulates of Sternberg's additive processes theory.