Analysis of hippocampal local field potentials by diffusion mapped delay coordinates.

Spatial navigation through novel spaces and to known goal locations recruits multiple integrated structures in the mammalian brain. Within this extended network, the hippocampus enables formation and retrieval of cognitive spatial maps and contributes to decision making at choice points. Exploration and navigation to known goal locations produce synchronous activity of hippocampal neurons resulting in rhythmic oscillation events in local networks. Power of specific oscillatory frequencies and numbers of these events recorded in local field potentials correlate with distinct cognitive aspects of spatial navigation. Typically, oscillatory power in brain circuits is analyzed with Fourier transforms or short-time Fourier methods, which involve assumptions about the signal that are likely not true and fail to succinctly capture potentially informative features. To avoid such assumptions, we applied a method that combines manifold discovery techniques with dynamical systems theory, namely diffusion maps and Takens' time-delay embedding theory, that avoids limitations seen in traditional methods. This method, called diffusion mapped delay coordinates (DMDC), when applied to hippocampal signals recorded from juvenile rats freely navigating a Y-maze, replicates some outcomes seen with standard approaches and identifies age differences in dynamic states that traditional analyses are unable to detect. Thus, DMDC may serve as a suitable complement to more traditional analyses of LFPs recorded from behaving subjects that may enhance information yield.

Age group differences on neuropsychological battery performance in a neuropsychiatric population: an international descriptive study with replications.

The relationship of age to performance on the Halstead-Reitan Neuropsychological Battery was examined in three samples drawn from neuropsychiatric populations: an initial sample of 217 subjects, a within-laboratory replication of 307 subjects, and a cross-national replication sample of 101 subjects. The results showed significant relationships of age to subtests of the Halstead-Reitan Battery involving problem-solving abilities and motor strength, which were replicated across the three samples. Verbal and perceptual subtests were not consistently related to age across samples. For those problem-solving and motor tests showing replicated correlations with age. mean scores are provided for three age groups (16-34, 35-54, and 55 and above), and group differences were tested with analysis of variance. These results help clarify for which measures age group differences are consistent in neuropsychiatric populations. Implications of these results for treatment program planning are discussed