Advance cueing produces enhanced action-boundary patterns of spike activity in the sensorimotor striatum.

One of the most characteristic features of habitual behaviors is that they can be evoked by a single cue. In the experiments reported here, we tested for the effects of such advance cueing on the firing patterns of striatal neurons in the sensorimotor striatum. Rats ran in a T-maze with instruction cues about the location of reward given at the start of the runs. This advance cueing about reward produced a highly augmented task-bracketing pattern of activity at the beginning and end of procedural task performance relative to the patterns found previously with midtask cueing. Remarkably, the largest increase in activity early during the T-maze runs was not associated with the instruction cues themselves, the earliest predictors of reward; instead, the highest peak of early activity was associated with the beginning of the motor period of the task. We suggest that the advance cueing, reducing midrun demands for decision making but adding a working-memory load, facilitated chunking of the maze runs as executable scripts anchored to sensorimotor aspects of the task and unencumbered by midtask decision-making demands. Our findings suggest that the acquisition of stronger task-bracketing patterns of striatal activity in the sensorimotor striatum could reflect this enhancement of behavioral chunking. Deficits in such representations of learned sequential behaviors could contribute to motor and cognitive problems in a range of neurological disorders affecting the basal ganglia, including Parkinson's disease.

Effects of level and background noise on interaural time difference discrimination for transposed stimuli.

Just-noticeable interaural time differences were measured for low-frequency pure tones, high-frequency sinusoidally amplitude-modulated (SAM) tones, and high-frequency transposed stimuli, at multiple levels with or without a spectrally notched diotic noise to prevent spread of excitation. Performance with transposed stimuli and pure tones was similar in quiet; however, in noise, performance was poorer for transposed stimuli than for pure tones. Performance with SAM tones was always poorest. In all conditions, performance improved slightly with increasing level. The results suggest that the equivalence postulated between transposed stimuli and pure tones is not valid in the presence of a spectrally notched background noise.