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.

Delayed kindling epileptogenesis and increased neurogenesis in adult rats housed in an enriched environment.

Environmental risk factors such as stressful experiences have long been recognized to affect seizure susceptibility, but little attention has been paid to the potential effects of improving housing conditions. In this study, we investigated the influence of an enriched environment on epileptogenesis. Epileptic susceptibility was assessed in animals housed in an enriched environment either before and during (group I) or only during (group II) a kindling procedure and in animals placed in isolated conditions (group III). The kindling paradigm provides a reliable assessment of the capacity to develop seizures following repeated daily low-frequency electrical stimulations. As both enriched environment and seizures are known to interfere with hippocampal neurogenesis, the number of newly generated dentate cells was assessed before and after the kindling procedure to investigate in more detail the relationship between epileptogenesis and neurogenesis. We found that susceptibility to developing epilepsy differed in animals housed in complex enriched environments and in those housed in isolated conditions. Kindling epileptogenesis occurred significantly later in animals housed in enriched conditions throughout the procedure (group I) than in animals from groups II and III. We also demonstrated that cells generated during kindling survived for at least 42 days and that these cells were more numerous on both sides of the brain following environmental enrichment than in rats housed in isolated conditions. As similar values were obtained regardless of the duration of the period of enrichment, these cellular changes may not play a major role in delaying kindling development. We suggest that the increase response in neurogenesis following seizures may be an adaptative rather an epileptogenic response.

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.