Abstract
BackgroundImpulsivity is a behavioural trait that comprises several distinct processes. It is a key feature of many psychopathologies such as mania, addictive disorders or attention deficit-hyperactivity disorders. To date, the aspects of impulsiveness involved in these pathologies have not yet been explicitly defined. In these disorders, sensation or drug seeking and cognitive deficits are closely related, but the nature of these relationships remains largely unknown. A new animal model of impulsiveness based on spontaneous inter-individual differences is proposed here to help clarify the relationship between characteristic aspects of impulsive-related pathologies.MethodsRats were divided into sub-groups according to their scores in three operant tasks with varying degrees of behavioural inhibition, timing and motor vs. cognitive impulsivity demands. These tasks included a fixed consecutive number schedule (ability to complete an action to receive a reinforcer), a multiple fixed-interval/extinction schedule of reinforcement (high level of responding), and a delayed reward task (delay discounting). In addition, measurements of locomotor responses to novelty and to amphetamine in a circular corridor, and working memory in an 8-arm radial maze were obtained.ResultsSubstantial behavioural inter-individual differences were observed in each task, whereas few inter-task relationships were found. Impulsive rats, as defined in a task requiring inhibition of premature responses, presented a higher increase in amphetamine-induced locomotion. Reduced working memory performance was only observed in hyperactive rats in an extinction schedule.ConclusionThis novel approach shows that distinct aspects of impulsiveness and hyperactivity can be expressed based on large inter-individual differences that vary from poorly to highly adapted behaviours ones in a normal population of rats. Inhibitory deficit was related to a higher response to psychostimulants a characteristic of rats predisposed to amphetamine self-administration and related to higher limbic dopaminergic activity, whereas working memory capacity was only related to hyperactivity. This approach allows for the identification of particular individuals presenting distinct behavioural characteristics of impulsive-related psychopathologies. These individuals may be of great interest in the modelling of these disorders and the exploration of their neurobiological bases.
Highlights
Impulsivity is a behavioural trait that comprises several distinct processes
Individual differences in impulsive-related behaviours Fixed consecutive number schedule (FCN8) Four rats were excluded from this analysis because they did not reach the criterion for the test phase
The mean chain length, ranging from 3.9 to 11.9 presses, was chosen, to classify rats into three groups: a first group in the upper quartile defining rats with low level of inhibition (LOWFCN, n = 8) contained all the rats with a mean chain length below 6, a second group in the lower quartile, defining rats with high level of inhibition (HIGHFCN, n = 9) with a mean chain length above 8, and the third contained the remainder defined as intermediate rats (INTFCN, n = 19) (Figure 1)
Summary
Impulsivity is a behavioural trait that comprises several distinct processes. It is a key feature of many psychopathologies such as mania, addictive disorders or attention deficithyperactivity disorders. The aspects of impulsiveness involved in these pathologies have not yet been explicitly defined In these disorders, sensation or drug seeking and cognitive deficits are closely related, but the nature of these relationships remains largely unknown. Impulsivity is mentioned in the DSM-IV diagnostic criteria as prominent in several psychiatric disorders, but it is never explicitly defined [3] It is a key aspect of mania, personality disorders and conduct disorders, and is regarded as the most relevant symptom in attention deficit-hyperactivity disorder (ADHD) [4,5,6]. Personality theorists have identified a factor called impulsive unsocialized sensationseeking, linking impulsivity to the sensation-seeking trait This factor has been shown to correlate with early onset of drug use and later drug abuse [12,13,14,15]
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