Hippocampal EEG, GABAergic interneurons, and principal cells were recorded simultaneously as rats foraged within one of three environments both before and after modulation of serotonergic inputs to ...the hippocampus. Median raphe microinjections of the 5-HT1a receptor agonist 8-OH-DPAT were made to produce inhibition of serotonergic neurons in this region. Such microinjections produced behavioral arousal and increases in the amplitude of hippocampal EEG theta. Consistent with the pattern of serotonergic innervation of the hippocampus, the GABAergic interneuron population was affected differentially by the microinjections. Principal cells were generally unaffected by the manipulation and maintained robust spatial firing correlates within the foraging environment. The results provide basic data on the relationship between serotonergic median raphe neurons and hippocampal activity in a behaving animal. The data suggest that behavioral responses to manipulation of the serotonergic system are mediated by brain regions other than the hippocampus or are mediated through changes in the activity of hippocampal interneurons.
Animals ranging from rats to humans can demonstrate cognitive map capabilities. We evolved weights in a biologically plausible recurrent neural network (RNN) using an evolutionary algorithm to ...replicate the behavior and neural activity observed in rats during a spatial and working memory task in a triple T-maze. The rat was simulated in the Webots robot simulator and used vision, distance and accelerometer sensors to navigate a virtual maze. After evolving weights from sensory inputs to the RNN, within the RNN, and from the RNN to the robot's motors, the Webots agent successfully navigated the space to reach all four reward arms with minimal repeats before time-out. Our current findings suggest that it is the RNN dynamics that are key to performance, and that performance is not dependent on any one sensory type, which suggests that neurons in the RNN are performing mixed selectivity and conjunctive coding. Moreover, the RNN activity resembles spatial information and trajectory-dependent coding observed in the hippocampus. Collectively, the evolved RNN exhibits navigation skills, spatial memory, and working memory. Our method demonstrates how the dynamic activity in evolved RNNs can capture interesting and complex cognitive behavior and may be used to create RNN controllers for robotic applications.
A method for detecting relationships between single-unit spike trains and local field potentials (LFPs) was developed and applied to recordings from rat cerebellum. LFPs were repeatedly filtered with ...a shifting frequency window. The resulting traces were transformed into peak-time point processes for comparison with spike trains using “relative-phase” analysis (Biol. Cybernet., in press). Discharge of some Purkinje cells was phase-related to LFP oscillations in the 2–
10
Hz
and 30–
50
Hz
frequency ranges. This analysis method revealed hidden coherency between spike-trains and LFPs. The findings suggest that cerebellar activity is, to some extent, temporally organized according to both slow and fast rhythms.
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