Bimanual coordination positively predicts episodic memory: A combined behavioral and MRI investigation.

Some people remember events more completely and accurately than other people, but the origins of individual differences in episodic memory are poorly understood. One way to advance understanding is by identifying characteristics of individuals that reliably covary with memory performance. Recent research suggests motor behavior is related to memory performance, with individuals who consistently use a single preferred hand for unimanual actions performing worse than individuals who make greater use of both hands. This research has relied on self-reports of behavior. It is unknown whether objective measures of motor behavior also predict memory performance. Here, we tested the predictive power of bimanual coordination, an important form of manual dexterity. Bimanual coordination, as measured objectively on the Purdue Pegboard Test, was positively related to correct recall on the California Verbal Learning Test-II and negatively related to false recall. Furthermore, MRI data revealed that cortical surface area in right lateral prefrontal regions was positively related to correct recall. In one of these regions, cortical thickness was negatively related to bimanual coordination. These results suggest that individual differences in episodic memory may partially reflect morphological variation in right lateral prefrontal cortex and suggest a relationship between neural correlates of episodic memory and motor behavior.

Focal cortical dysplasias in autism spectrum disorders.

BACKGROUND: Previous reports indicate the presence of histological abnormalities in the brains of individuals with autism spectrum disorders (ASD) suggestive of a dysplastic process. In this study we identified areas of abnormal cortical thinning within the cerebral cortex of ASD individuals and examined the same for neuronal morphometric abnormalities by using computerized image analysis. RESULTS: The study analyzed celloidin-embedded and Nissl-stained serial full coronal brain sections of 7 autistic (ADI-R diagnosed) and 7 age/sex-matched neurotypicals. Sections were scanned and manually segmented before implementing an algorithm using Laplace's equation to measure cortical width. Identified areas were then subjected to analysis for neuronal morphometry. Results of our study indicate the presence within our ASD population of circumscribed foci of diminished cortical width that varied among affected individuals both in terms of location and overall size with the frontal lobes being particularly involved. Spatial statistic indicated a reduction in size of neurons within affected areas. Granulometry confirmed the presence of smaller pyramidal cells and suggested a concomitant reduction in the total number of interneurons. CONCLUSIONS: The neuropathology is consistent with a diagnosis of focal cortical dysplasia (FCD). Results from the medical literature (e.g., heterotopias) and our own study suggest that the genesis of this cortical malformation seemingly resides in the heterochronic divisions of periventricular germinal cells. The end result is that during corticogenesis radially migrating neuroblasts (future pyramidal cells) are desynchronized in their development from those that follow a tangential route (interneurons). The possible presence of a pathological mechanism in common among different conditions expressing an autism-like phenotype argue in favor of considering ASD a "sequence" rather than a syndrome. Focal cortical dysplasias in ASD may serve to explain the high prevalence of seizures and sensory abnormalities in this patient population.

Gyral window mapping of typical cortical folding using MRI.

Using the NIH Pediatric MRI Data Repository for normative developmental studies, white matter depth within the gyri of the frontal, temporal, parietal, and occipital lobes, and of the left and right hemisphere was identified for 312 typically developing children and young adults (168 male and 144 female) between 4 and 23 years of age. There was no significant age difference between male and female groups overall (F(1,867) = 0.0002; p = 0.99) or per-visit (F(2,867) = 2.18; p = 0.86). There was significant dependence of gyral window upon age (F(1,6544) = 115, p < 0.0001), lobe (F(3,6544) = 229, p < 0.0001), hemisphere (F(1,6544) = 5.23, p = 0.022), age*sex (F(1,6544) = 13.8, p = 0.0002), age*lobe (F(3,6544) = 120, p = 0.0001), and age*hemisphere (F(1,6544) = 4.41, p = 0.036). Gyrification increased with age in both males and females in the frontal, temporal and parietal lobes with opposite effects observed in the occipital lobe. Relative gyral depth, as measured in this study, was significantly (p < 0.0001) inversely correlated with gyrification index. Previous studies relate gyral window measurements to the differential expression of short and long corticocortical projections. Our results therefore suggest that the pattern of corticocortical connections is malleable during the first two decades of development.