Cognitive function is the capacity of the human brain to process information coming from the outside and internal world, and consequently to program the most opportune behavior (1). This capacity involves the ability to remain in contact with the outside world (through the function of vigilance), to select and focus information (through the function of attention), and to memorize data (through the function of memory). In this way, cognitive function gives humans the opportunity to become aware of themselves and to solve problems: something that we also call intelligence. An impairment in cognitive function may be seen as a reduction in the capacity of learning of children or reduction in the intellectual ability of adults. We normally call such situations learning disability in children (which, at least in some countries, is different from mental retardation), and deterioration or dementia in adults or people who have already acquired mental capacity. In some countries, such as United Kingdom, learning disability is used for defining both mental retardation and the learning disorders. This is not universally the case. The DSM IV (2) definition of learning disorders (DSM IV 315.00, 315.1, 315.2, and 315.9) includes a significant disturbance in academic achievement or daily living activities that require reading, mathematic, or writing skills. Learning disorders are different from mental retardation, which is defined not as a necessarily lifelong disorder, characterized by the combination of a low cognitive ability and diminished social and adaptive competence (DSM IV 317–319). In epilepsy, there is a risk of implying the presence of a learning disorder in a case of mental retardation, as well as failing to distinguish patients who are affected only by a specific learning disorder but do not have mental retardation. For example, it is known that an epileptic focus may cause dysfunction of a given specific performance that coincides with the cortical area involved, without causing mental retardation. Furthermore, in the developmental age when cognitive performance has not been definitely acquired, a dysfunction in a specific cognitive performance may cause a disequilibrium of the complex system of mental (cognitive) development. This may suggest an apparently true mental retardation, which may completely improve if this specific cognitive dysfunction is adequately treated early. In most parts of the world, we tend to define mental retardation as a situation involving an abnormal IQ, and a learning disorder as one involving a normal IQ. Learning disorders are linked to various other disturbances that must be separately classified: for example, attention deficit/hyperactivity disorder (ADHD; DSM IV 314.00–314.01), which may or may not be associated with behavioral or mood disturbances (DSM IV 312.8). In populations without epilepsy, we know that learning disorders are associated with other disorders, such as conduct disorders, major depressive disorders, dysthymic disorders, and oppositional defiant disorder in 10–25% of cases. Learning disorders and behavioral disorders are often linked, both in childhood and in adults. Although it is true that behavioral or mood disorders may be seen as symptomatic expressions of a cognitive impairment with epilepsy, it is also true that behavioral or mood disorders may be the cause of a reduced learning ability. This question of a link between convulsive disorders and behavioral, mood, or personality disorders is also discussed in adults. Perini et al. (3) recently reported a good correlation between temporal lobe epilepsy and interictal affective and personality disturbance, and well-directed violence and self-destructive behavior have recently been described by Kanemoto et al. (4) in postictal psychosis. In both of these studies, epilepsy was not an adjustment reaction to a chronic disease but a specific etiologic factor. Thus, there is no doubt that a disproportionate percentage of children with epilepsy have learning disorders and behavioral problems (5) that are not necessarily related to mental retardation. Both in children and adults, the concept that epilepsy is invariably associated with progressive intellectual deterioration prevailed during the first half of the twentieth century (5), but we do not think this is the case anymore. A large proportion (∼50%) of the children with epilepsy have some schooling difficulties (6,7), but <1% attend special epilepsy schools. It was recently reported that ∼20% of the epilepsy population have mental retardation (8–10), and ∼20–50% of mentally retarded people have epilepsy (depending on the severity of the handicap; see Lhatoo and Sander in this issue) (11,12). In reality, only a small subgroup of children with epilepsy shows stable decreases in IQ. Besag (13) recently demonstrated that a declining IQ at any given moment in a patient with epilepsy does not necessarily mean a loss of skills, but simply implies that the child is not developing at the expected rate. The mental age lags behind the chronologic age. When a decrease in mental age does reflect a loss of skills, there is usually an identifiable cause, such as brain damage or stable brain dysfunction. In these cases, there is a statistically significant relationship between the slowing in the increase in mental age and the presence of overnight EEG abnormalities and/or frequent spike-and-wave discharges (13). Any child who loses skills must be investigated further, unless a cause has already been identified. According to some authors, the lag that can develop between mental and chronologic age is more pronounced in older children, and in children with an earlier seizure onset, a higher lifetime total number of seizures, or multiple seizure types (14). There is some evidence indicating that children younger than 10 years at the time of onset gain skills less than those with an age at onset of older than 10 years (15). Moreover, patients with symptomatic epilepsies and mixed seizures have a significantly lower initial IQ scores (16). Learning disorders that may occur during epilepsy can be classified into two categories: either "state-dependent" (potentially treatable and reversible) or "permanent," although we cannot exclude the possibility of the simultaneous presence of both types. The prevalence of state-dependent or permanent learning disorders is not satisfactorily known. Brain damage or stable brain dysfunction is mainly associated with permanent learning disorders. Epilepsy itself or the medication used to treat it may lead to state-dependent learning disorders, as may associated mood disorders or psychoses, a low level of self-perception and expectation, or reduced learning opportunities. Regarding epilepsy itself, various situations can be recognized in causing a state-dependent learning disorder: -ictal changes: the main example of this learning disorder would be the nonconvulsive status epilepticus, which may continue unrecognized for months or years. -periictal changes: this situation refers to subjects who have so many seizures every day that they do not have time to recover from one to another. Prodromes and aurae also may be considered part of these periictal changes. -the presence of frequent subtle seizures and the direct effects of interictal EEG epileptiform discharges (transitory cognitive impairment): If these are very frequent, they may amount to nonconvulsive status epilepticus. It has been suggested that, if allowed to continue for a long time, state-dependent learning disorders may produce permanent learning disorders. Strong evidence for this comes from some rare models of epilepsy [e.g., the Landau–Kleffner syndrome (LK), continuous spike wave during sleep (CSWS), and probably drug-resistant partial lesional epilepsies in children and adults]. These models suggest the need for new studies to address the effect of frequent epileptiform EEG discharges, with or without clinical seizures, on causing learning disorders. It is also necessary to discover whether state-dependent learning disorders are treatable and reversible: for example, some evidence shows that intervention in LK can reverse the speech impairment in some cases [and we observed two patients with LK and atypical absences who completely receded after a variable course after 8–10 years]. State-dependent learning disorders may be a consequence of transitory cognitive impairment (TCI), associated with focal and/or generalized specific epileptiform EEG discharges. This has been recognized since 1939, when Schwab (17) demonstrated that generalized spike–wave discharges, without any apparent clinical concomitants, may be associated with a simultaneous decline in cognitive function. TCI also was found in 1957 by Kooi and Hovey (18), who studied a case involving focal discharges. The fact that these subclinical or "larval" discharges are accompanied by a TCI, which, if not recognizable from the patient's spontaneous behavior, can be detected by appropriate psychological tests during EEG monitoring, was ascertained by Binnie (19). TCI is most readily demonstrated by giving difficult cognitive tasks and during generalized regular spike–wave discharges lasting >3 s, but it can also be found in the case of briefer and focal discharges. In this latter case, the errors are more specific: left-sided focal discharges are more likely to produce errors in verbal tasks, whereas right-sided discharges are associated with the impaired handling of nonverbal material. This means that TCI is not only a consequence of global inattention, and it has been hypothesized that, in these cases, the errors may be due to a working memory disorder (20). The effect of TCI accompanying subclinical EEG discharges on everyday functioning is still uncertain and needs further investigation, but there is experimental evidence that subclinical discharges may be accompanied by a disruption of educational skills in children, and that antiepileptic drug (AED) suppression of discharges is associated with improvement of cognitive function. We observed the case of a child with a very active right temporooccipital focus with a specific deficit in visuospatial performance, who regained his abilities after treatment with lamotrigine (LTG) and a concomitant reduction of >70% in spike activity on the EEG. Certainly the extent to which such subtle manifestations affect learning and behavior remains unknown, and there are many controversial questions to be asked regarding the importance of subtle manifestations of epilepsy on learning and behavior. In addition, it is possible that some children diagnosed as having ADHD or autism may actually be affected by undiagnosed manifestations of epilepsy. We recently observed a 9-year-old child who was brought to our attention after he had received psychotherapy for >3 years after a diagnosis of autism. An EEG showed the presence of very frequent generalized spike–wave sequences, especially during sleep. It is also commonly observed that undiagnosed severe epileptic conditions, such as some frontal lobe epilepsies with subcontinuous specific EEG activity (including rapid activity lasting between 1 and 1.5 s), are subsequently associated with the onset of severe behavioral disturbances (sometimes with psychotic symptoms), or schizophrenia-like or autism-like syndromes. This question occurs not only in children, but also in adults. The existence of situations such as these underline the need to clarify the causative role of epilepsy or the presence of nonconvulsive EEG epileptiform discharges in childhood and adult behavioral problems. We believe that the use of the EEG in children and in adults showing behavioral or learning disturbances must again be reconsidered with more attention. Similarly, we believe that the issue of intervening to ameliorate interictal EEG discharges must be reconsidered. This needs considerable care and must be evaluated in each patient, because it is difficult to ensure that the drugs themselves do not disrupt cognitive processing. The causes of cognitive and behavioral impairment are multifactorial, and a large number of clinical studies have been carried out with the aim of identifying the relative contribution of AEDs. This area of research has been characterized by an unusually large number of methodologic challenges, and the results have often been contradictory. AEDs may cause state-dependent learning disorders, but the evidence is so far largely anedoctal. Although a large number of studies have been published, we can still only tentatively suggest that drugs such as LTG, carbamazepine (CBZ), oxcarbamazepine, valproate, and felbamate are less often reported as affecting cognitive functions, in contrast to some other drugs such as phenobarbital, phenytoin, and clonazepam, and so there is still a need for evidence-based guidelines (21) in this area, and the effect of many of the new drugs on cognition must be investigated. Some recent studies have compared the efficacy and the presence of cognitive and behavioral side effects of various AEDs. For example, in adults it has been found that the efficacy against seizures of vigabatrin (VGB), LTG, and gabapentin is similar, but that VGB is associated with a higher incidence of behavioral problems (22). The results of other studies support the hypothesis that the cognitive profile of LTG is similar to that of CBZ, insofar as the addition of LTG did not lead to any statistically significant decrease in the memory, attentional or mental speed test scores, and most of the changes were in the positive direction (23). Burton and Harden (24) assessed the effect of 3 months' treatment with topiramate (TPM) on attention and reported a significant correlation between TPM dose and the forward digit span, the higher dose being associated with poor attention. Because an AED may improve learning by reducing the number of EEG discharges or the frequency of seizures, but at the same time, it may impair learning as a result of its direct side effects: sleepiness, slowed reactions, attention deficit, and so on, we must not forget the relevance of the clinical observations of each case. Learning disorders must be considered in the preoperative preparation and postoperative rehabilitation of patients with epilepsy. In the preoperative phase, it is important to consider the effect that the surgical ablation of the area of the epileptic focus may have on the processes of learning. The ablation of an epileptogenic area generally produces positive effects because it eliminates the negative consequences of the epileptic discharges that go from this to other parts of the brain. However, if the area of the epileptogenic focus has not completely lost its own primary function, the same ablation may lead to a functional deficit. In this case, even a satisfactory improvement in seizure frequency may lead to very negative postoperative results. Postoperative rehabilitation must take into account the developmental level of the individual, and may take weeks or months of intensive specialist input, but provided that this is carefully planned and delivered, the outcome can be very good. The relationships between learning disorders and epilepsy are still an underexplored and discussed area. Tentatively, we may summarize the actual picture as follows: epilepsy may be associated with learning disorders and behavioral or mood disorders; behavior and learning are often linked: behavioral changes may result from temporary or permanent cognitive deficits; learning disorders in epilepsy may be "state dependent" or "permanent"; it has been suggested that state-dependent learning disorders may produce permanent learning disorders; the prevalence of both these conditions is not known; strong evidence now shows that very frequent overnight and daytime epileptiform discharges may eventually result in state-dependent learning disorders; epilepsy itself, AEDs, and more than one social factor may influence the onset of learning disorders; even if a large percentage of children with epilepsy have school difficulties, only a minority shows a loss of skills or a decreasing IQ; for children in whom actual loss of skills occurs, it is essential to look for a specific cause, and to plan an ad hoc program; it has been suggested that in adults, a real loss of skills may be more frequently seen; and mental retardation normally presumes the existence of brain damage and/or permanent dysfunction.
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Cornaggia et al. (2001) studied this question.
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