Temporal processing is fundamental to many aspects of cognition and behavior. For behavior to be adaptive, an animal must be able to predict not only where, but also when an event is likely to occur. Cortico-basal ganglia circuits have been implicated as a crucial brain area for timing and time perception, especially for cognitively controlled timing processes. I studied various types of timing behaviors across species (humans and rats) using various methods (electrophysiology, Bayesian analysis, and computational simulation) and in relation to brain disorders (Parkinson’s disease and obsessive-compulsive disorder).
Ordinal comparison task in humans and rats
Timing behaviors are strongly evolutionarily conserved and rely on the basal ganglia; thus, they provide a strong platform for cross-species investigations of behavioral control processes. Both human (Gu & Meck, 2011) and rats (Gu et al., 2018) can do ordinal comparison of temporal durations and show memory-mixing effects. Memory-mixing effect (‘Vierordt’s Law) describes biases in temporal judgement or reproductions, where individuals tend to underestimate long durations and overestimate short durations by anchoring their responses towards the mean of the signal duration distribution.
Neural oscillations underlying interval timing
To investigate the nature of neural oscillations during the temporal processing, I recorded local field potentials from the cortex and striatum in rats during an ‘ordinal-comparison of durations‘ task. During the encoding of the first signal duration (standard), increases in low-frequency neural oscillations, including theta and delta, were observed in both cortex and striatum (Gu et al., 2018).
Interval timing and working memory
Interval timing and working memory are critical components of cognition that are supported by neural oscillations in prefrontal-striatal-hippocampal circuits. To understand the mechanisms of neural oscillations underlying the shared properties of interval timing and working memory, I developed a coupled excitatory-inhibitory oscillation (EIO) model of temporal processing (Gu et al., 2015; Teki et al., 2017). This model explains how interval timing and working memory can originate from the same oscillatory processes, but differ in terms of which dimension of the neural oscillation is utilized for the extraction of item, temporal order, and duration information.
Timing behaviors in clinical populations
Interval timing behaviors are sensitive to both temporal context and changes in dopamine levels. Patients with Parkinson’s disease (PD) show distorted timing behaviors, and I used a Bayesian model to understand this behavior in relation to the reduced levels of dopamine. The simulated result suggests that decreased dopamine levels increase the uncertainty of duration measures, and this will shift optimal timing behaviors towards a greater reliance on a statistical representation of previous durations in a temporal reproduction task (increased memory-mixing effect) (Gu et al., 2016).
Altered timing behaviors are also shown in a rodent model of OCD (Gu et al., 2011). Quinpirole-sensitized rats, a rodent model of OCD, exhibit an excessive checking, and perseverative reward-related behaviors. These OCD model rats showed excessively repetitive timing behaviors related to food-cup checking (goal-directed behavior), while lever press behaviors (habitual behavior) were less affected.
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