آماده سازی زمانی، بازداری پاسخ و تکانشگری

Temporal preparation and impulsivity involve overlapping neural structures (prefrontal cortex) and cognitive functions (response inhibition and time perception), however, their interrelations had not been investigated. We studied such interrelations by comparing the performance of groups with low vs. high non-clinical trait impulsivity during a temporal preparation go no-go task. This task measured, in less than 10 min, how response inhibition was influenced both by temporal orienting of attention (guided by predictive temporal cues) and by sequential effects (produced by repetition/alternation of the duration of preparatory intervals in consecutive trials). The results showed that sequential effects produced dissociable patterns of temporal preparation as a function of impulsivity. Sequential effects facilitated both response speed (reaction times – RTs – to the go condition) and response inhibition (false alarms to the no-go condition) selectively in the low impulsivity group. In the high impulsivity group, in contrast, sequential effects only improved RTs but not response inhibition. We concluded that both excitatory and inhibitory processing may be enhanced concurrently by sequential effects, which enables the temporal preparation of fast and controlled responses. Impulsivity could hence be related to less efficient temporal preparation of that inhibitory processing.

Regular changes in the environment afford the anticipation and preparation of efficient behavioural responses to forthcoming events. Response preparation is a transient process, which requires several tens of milliseconds to develop and decays shortly after reaching a maximum (Bertelson, 1967). However, the time course of the optimal state of preparation can be flexibly adjusted to coincide with the moment at which a task-relevant event (target) is expected to occur. This adjustment is generally called “temporal preparation” and its consequences are revealed by improvements in task performance. Temporal preparation can be controlled voluntarily, “temporal orienting of attention” (Coull & Nobre, 1998), if individuals are provided with explicit and predictive temporal information about when a target is going to appear after a preparatory interval (e.g., early: after 400 ms, or late: after 1400 ms; see Correa (2010), for a review). Temporal preparation can also be driven by previous experiences of response preparation (Los & Van den Heuvel, 2001), which is known as “sequential effects”. For example, response preparation for a target appearing after a short (400 ms) preparatory interval is stronger when that interval involves a repetition of a previous short interval rather than a switch from a previous long (1400 ms) interval, even when the sequence of short and long preparatory intervals is completely unpredictable (Woodrow, 1914). These two mechanisms of temporal preparation have been dissociated in both behavioural and electrophysiological research (Correa et al., 2004 and Los and Heslenfeld, 2005). In a recent neuropsychological study we have reported a selective impairment in temporal orienting but not in sequential effects as a consequence of lesions in the right prefrontal cortex (Triviño, Correa, Arnedo, & Lupiáñez, 2010). The involvement of the prefrontal cortex is important here because clinical and non-clinical impulsive individuals show anatomical and physiological differences as compared to control participants in this brain area (see Brennan and Arnsten (2008), for a review; Matsuo et al., 2009). Impulsivity is a personality trait that has been defined as “a predisposition toward rapid, unplanned reactions to internal or external stimuli without regard to the negative consequences of these reactions to the impulsive individuals or to others” (Moeller, Barratt, Dougherty, Schmitz, & Swann, 2001). In experimental contexts of clinical impulsivity (e.g., attention deficit and hyperactivity disorder, ADHD), impulsivity can be operationalised in terms of a behavioural deficit in response inhibition tasks (Casey et al., 1997). Thus, the common role of the prefrontal cortex in both temporal preparation and impulsivity suggests a close interrelation between these two constructs. However, to our knowledge, this relationship had not been considered or tested so far. Temporal preparation and impulsivity additionally share cognitive processes, such as response inhibition and time perception. Response inhibition is influenced by impulsivity, as subjects with high trait impulsivity as measured by personality questionnaires have difficulties to inhibit a prepotent response in the stop-signal task (Logan, Schachar, & Tannock, 1997); likewise, inhibitory processes may play a role during temporal preparation (e.g., controlling excitatory neural activity, Correa and Nobre, 2008 and Davranche et al., 2007). Time perception is also influenced by impulsivity, which could contribute to the inability to wait for appropriate moments that is characteristic of this clinical disorder (see Wittmann and Paulus (2008), for a review); likewise, accurate time perception is a requisite for temporal preparation (Klemmer, 1956). The functional overlapping between response inhibition and time perception is not surprising given the common involvement of the prefrontal cortex in both cognitive processes (Coull et al., 2004, Harrington et al., 1998, Narayanan et al., 2006 and Rubia et al., 2003). This led us to hypothesise that impulsivity, which shares such prefrontal functions, may influence temporal preparation. Although interactions between impulsivity and temporal preparation should be most evident under clinical conditions of impulsivity, we still expected to find differences in behavioural performance during temporal preparation tasks as a function of trait impulsivity according to previous research showing behavioural and brain differences in non-clinical samples (Logan et al., 1997 and Matsuo et al., 2009). The current experiment tested this hypothesis by comparing both temporal orienting (temporal cue validity effects) and sequential effects (duration of previous preparatory interval × current interval interaction) in non-clinical participants with high vs. low impulsivity traits. We expected that temporal orienting but not sequential effects would be influenced by impulsivity, according to Triviño et al.’s findings (2010) in prefrontal patients. The use of a response inhibition go no-go task (presented on each trial after the preparatory interval), and the inclusion of a temporal estimation task (presented in the middle and at the end of the experiment), further enabled us to test whether response inhibition and time perception varied with trait impulsivity. If so, we should find both less efficient response inhibition during the go no-go task and a larger perceptual bias in the temporal estimation task in the high impulsivity group as compared to the low impulsivity group. From a rather pragmatic perspective, an important aim of this experiment was to develop a shortened version of the task that was appropriate for diagnosing temporal preparation skills. That is, we tested whether this novel task could measure temporal orienting and sequential effects as reliably as previous versions (Correa et al., 2006 and Triviño et al., 2010) in less than 10 min.