The Alteration of Emotion Regulation Precedes the Deficits in Interval Timing in the BACHD Rat Model for Huntington Disease

Timing behavior in genetic murine models of neurological and psychiatric diseases

How timing behavior is altered in different neurodevelopmental and neurodegenerative disorders is a contemporary research question. Genetic murine models (GMM) that offer high construct validity also serve as useful tools to investigate this question. But the literature on timing behavior of different GMMs largely remains to be consolidated. The current paper addresses this gap by reviewing studies that have been conducted with GMMs of neurodevelopmental (e.g. ADHD, schizophrenia, autism spectrum disorder), neurodegenerative disorders (e.g., Alzheimer's disease, Huntington's disease) as well as circadian and other mutant lines. The review focuses on those studies that specifically utilized the peak interval procedure to improve the comparability of findings both within and between different disease models. The reviewed studies revealed timing deficits that are characteristic of different disorders. Specifically, Huntington's disease models had weaker temporal control over the termination of their anticipatory responses, Alzheimer's disease models had earlier timed responses, schizophrenia models had weaker temporal control, circadian mutants had shifted timed responses consistent with shifts in the circadian periods. The differences in timing behavior were less consistent for other conditions such as attention deficit and hyperactivity disorder and mutations related to intellectual disability. We discuss the implications of these findings for the neural basis of an internal stopwatch. Finally, we make methodological recommendations for future research for improving the comparability of the timing behavior across different murine models.

Respiration and brain neural dynamics associated with interval timing during odor fear learning in rats

In fear conditioning, where a conditioned stimulus predicts the arrival of an aversive stimulus, the animal encodes the time interval between the two stimuli. Here we monitored respiration to visualize anticipatory behavioral responses in an odor fear conditioning in rats, while recording theta (5–15 Hz) and gamma (40–80 Hz) brain oscillatory activities in the medial prefrontal cortex (mPFC), basolateral amygdala (BLA), dorsomedial striatum (DMS) and olfactory piriform cortex (PIR). We investigated the temporal patterns of respiration frequency and of theta and gamma activity power during the odor-shock interval, comparing two interval durations. We found that akin to respiration patterns, theta temporal curves were modulated by the duration of the odor-shock interval in the four recording sites, and respected scalar property in mPFC and DMS. In contrast, gamma temporal curves were modulated by the interval duration only in the mPFC, and in a manner that did not respect scalar property. This suggests a preferential role for theta rhythm in interval timing. In addition, our data bring the novel idea that the respiratory rhythm might take part in the setting of theta activity dynamics related to timing.

The Peak Interval Procedure in Rodents: A Tool for Studying the Neurobiological Basis of Interval Timing and Its Alterations in Models of Human Disease

Animals keep track of time intervals in the seconds to minutes range with, on average, high accuracy but substantial trial-to-trial variability. The ability to detect the statistical signatures of such timing behavior is an indispensable feature of a good and theoretically-tractable testing procedure. A widely used interval timing procedure is the peak interval (PI) procedure, where animals learn to anticipate rewards that become available after a fixed delay. After learning, they cluster their responses around that reward-availability time. The in-depth analysis of such timed anticipatory responses leads to the understanding of an internal timing mechanism, that is, the processing dynamics and systematic biases of the brain's clock. This protocol explains in detail how the PI procedure can be implemented in rodents, from training through testing to analysis. We showcase both trial-by-trial and trial-averaged analytical methods as a window into these internal processes. This protocol has the advantages of capturing timing behavior in its full-complexity in a fashion that allows for a theoretical treatment of the data.

Beyond Freezing: Temporal Expectancy of an Aversive Event Engages the Amygdalo–Prefronto–Dorsostriatal Network

During Pavlovian aversive conditioning, a neutral conditioned stimulus (CS) becomes predictive of the time of arrival of an aversive unconditioned stimulus (US). Using a paradigm where animals had to discriminate between a CS+ (associated with a footshock) and a CS− (never associated with a footshock), we show that, early in training, dynamics of neuronal oscillations in an amygdalo–prefronto–striatal network are modified during the CS+ in a manner related to the CS–US time interval (30 or 10 s). This is the case despite a generalized high level of freezing to both CS+ and CS−. The local field potential oscillatory power was decreased between 12 and 30 Hz in the dorsomedial striatum (DMS) and increased between 55 and 95 Hz in the prelimbic cortex (PL), while the coherence between DMS, PL, and the basolateral amygdala was increased in the 3–6 Hz frequency range up to the expected time of US arrival only for the CS+ and not for the CS−. Changing the CS–US interval from 30 to 10 s shifted these changes in activity toward the newly learned duration. The results suggest a functional role of the amygdalo–prefronto–dorsostriatal network in encoding temporal information of Pavlovian associations independently of the behavioral output.

Interval timing deficits and their neurobiological correlates in aging mice

Age-related neurobiological and cognitive alterations suggest that interval timing (as a related function) is also altered in aging, which can, in turn, disrupt timing-dependent functions. We investigated alterations in interval timing with aging and accompanying neurobiological changes. We tested 4-6, 10-12, and 18-20 month-old mice on the dual peak interval procedure. Results revealed a specific deficit in the termination of timed responses (stop-times). The decision processes contributed more to timing variability (vs. clock/memory process) in the aged mice. We observed age-dependent reductions in the number of dopaminergic neurons in the VTA and SNc, cholinergic neurons in the medial septum/diagonal band (MS/DB) complex, and density of dopaminergic axon terminals in the DLS/DMS. Negative correlations were found between the number of dopaminergic neurons in the VTA and stop times, and the number of cholinergic neurons in MS/DB complex and the acquisition of stop times. Our results point at age-dependent changes in the decisional components of interval timing and the role of dopaminergic and cholinergic functions in these behavioral alterations.

Interval timing is disrupted in female 5xFAD mice: An indication of altered memory processes

Temporal information processing in the seconds-to-minutes range is disrupted in patients with Alzheimer's disease (AD). In this study, we investigated the timing behavior of the 5xFAD mouse model of AD in the peak interval (PI) procedure. Nine-month-old female mice were trained with sucrose solution reinforcement for their first response after a fixed-interval (FI) and tested in the inter-mixed non-reinforced PI trials that lasted longer than FI. Timing performance indices were estimated from steady-state timed anticipatory nose-poking responses in the PI trials. We found that the time of maximal reward expectancy (peak time) of the 5xFAD mice was significantly earlier than that of the wild-type (WT) controls with no differences in other indices of timing performance. These behavioral differences corroborate the findings of previous studies on the disruption of temporal associative memory abilities of 5xFAD mice and can be accounted for by the scalar timing theory based on altered long-term memory consolidation of temporal information in the 5xFAD mice. This is the first study to directly show an interval timing phenotype in a genetic mouse model of AD.