Inattention is one of the main symptoms of attention-deficit/hyperactivity disorder (ADHD). Children with ADHD show weaker prepulse inhibition (PPI), which suggests inadequate sensorimotor gating, or sensory gating. Sensorimotor gating is an automatic and involuntary inhibitory system for canceling unnecessary cognitive processing. Research shows that spontaneously hypertensive rats (SHR) used in animal models of ADHD exhibit hyperactivity and weaker PPI. In this study, to examine sensory gating in SHR, we recorded auditory event-related potentials (ERP) in their cerebral cortex. The SHR did not exhibit significantly attenuated P50 suppression-like responses compared to the control group. On the other hand, the SHR exhibited significantly altered overall waveforms to the second stimulus compared to the control. This may indicate the gating characteristics of the SHR. Thus, it is important to consider sensory gating not only as a change in amplitude of ERP but also as a temporal waveform alteration.

The peak-interval (PI) procedure is a temporal discrimination task used with animals, significantly affected by the hippocampus and the striatum. We focused on N-methyl-D-aspartate (NMDA) receptors because they are found at high concentrations in the hippocampus, and investigated the effects of D, L-2-amino-5-phosphonopentanoic acid (AP5), an NMDA receptor antagonist, in the PI procedure. Rats were given acute administrations of AP5 into indusium griseum after PI training for 30 s. The result indicated that AP5 induced a rightward response distribution shift suggesting that AP5 produced an overestimation of the criterion time. This finding implies that NMDA receptors surrounding indusium griseum affect the PI procedure’s timing behavior, which indicates NMDA receptors’ role in time perception.

We investigated the effect of a blockade in the D1 dopamine receptor (D1DR) of the bilateral medial prefrontal cortex on interval timing in rats. A peak-interval (PI) procedure consisting of a standard operant task using food pellets was conducted to evaluate interval timing precision and accuracy. Compared to the vehicle (0.0 µg), the D1DR antagonist SCH23390 (0.5 µg) flattened the response rate curve and decreased the discrimination index (DI), an index of temporal precision, without altering the within-trial response rate. Neither the response rate curve nor DI changed after administering 1.5 µg SCH23390, although the within-trial response rate decreased. We also observed a similar overall decrease in a different timing-free operant task. In contrast, temporal accuracy indices remained constant across all doses. These results suggest that the D1DR blockade in the medial prefrontal cortex of rats decreases the precision but not the accuracy of interval timing.

The retrosplenial cortex is a brain area extending to the most caudal part of the medial parietal area around the corpus callosum. The human retrosplenial cortex is thought to be involved in a variety of cognitive functions such as navigation and episodic memory. In rodents, the retrosplenial cortex has connections to other brain regions crucial for processing spatial information. The role of the retrosplenial cortex in spatial problem-solving has been examined by using various spatial tasks. We reviewed studies on the role of the retrosplenial cortex in spatial tasks by focusing on lesion studies of rats and discussed its functions. Based on the review, we suggest that the retrosplenial cortex is involved in processing spatial information, especially spatial memory, utilization of allocentric cues, and integrating and switching cue use for spatial problem-solving.

Optogenetics is a recently developed biological tool to artificially control the activities of targeted neural populations and neural projections in millisecond time resolution by intracerebral light irradiation in freely moving animals. In this review, we have briefly explained: (1) the mechanisms of light-gated microbial channels or pumps permitting light-induced membrane potential changes, and (2) the experimental procedures for expressing these proteins in target brain regions to activate or inactivate specific cell populations. We have also introduced recent findings revealed by optogenetics, particularly focusing on studies investigating how psychological theories are embedded in specific brain circuits. Optogenetics will greatly expand our understanding of neural mechanisms underlying various kinds of behaviors.