The Role of Acetylcholine in Attention in Turtles (Chrysemys picta).

Research on mammals and turtles has suggested that acetylcholine is involved in attention in these groups. Two experiments investigated the ability of painted turtles (Chrysemys picta) to ignore irrelevant stimuli when the basal forebrain acetylcholine system was compromised. In experiment 1, turtles given lesions of the basal magnocellular cholinergic nucleus (NBM) or sham lesions were tested on a go/no go discrimination between horizontal and vertical stripes with or without irrelevant inserts in the box. The irrelevant inserts were blue and white checked walls and green carpet on the floor. The group with lesions of the NBM and no irrelevant inserts had no difficulty learning the task, but the lesioned group with irrelevant inserts was impaired on the discrimination. The sham-lesioned group was not impaired by the presence of irrelevant inserts. In experiment 2, turtles were given either the acetylcholine muscarinic receptor blocker scopolamine or saline and tested on the same task. The turtles given scopolamine had no difficulty learning the task in the absence of irrelevant inserts, but they were severely impaired when irrelevant inserts were present. The irrelevant inserts did not affect the learning of control turtles given saline. These findings provide evidence that acetylcholine enhances turtles' ability to orient to relevant stimuli and suggest that its role in learning and memory may be to allow animals to orient to the stimuli relevant to a task and to ignore irrelevant stimuli.

Investigation of superior longitudinal fasciculus fiber complexity in recent onset psychosis.

BACKGROUND: Standard diffusion tensor imaging measures (e.g., fractional anisotropy; FA) are difficult to interpret in brain regions with crossing white-matter (WM) fibers. Diffusion spectrum imaging (DSI) can be used to resolve fiber crossing, but has been difficult to implement in studies of patients with psychosis given long scan times. METHODS: We used four fold accelerated compressed sensing to accelerate DSI acquisition to investigate the superior longitudinal fasciculus (SLF) in 27 (20M/7F) patients with recent onset psychosis and 23 (11M/12F) healthy volunteers. Dependent measures included the number of crossing fiber directions, multi directional anisotropy (MDA), which is a measure sensitive to the anisotropy of the underlying water diffusion in regions of crossing fibers, generalized FA (GFA) computed from the orientation distribution function, FA and tract volume. RESULTS: Patients demonstrated a greater number of crossing WM fibers, lower MDA, GFA and FA in the left SLF compared to healthy volunteers. Patients also demonstrated a reversal in the normal (R>L) asymmetry of crossing fiber directions in the SLF and a lack of normal (L>R) asymmetry in MDA, GFA and FA compared to healthy volunteers. Lower GFA correlated significantly (p<0.05) with worse overall neuropsychological functioning; posthoc tests revealed significant effects with verbal functioning and processing speed. CONCLUSIONS: Our findings provide the first in vivo evidence for abnormal crossing fibers within the SLF among individuals with psychosis and their functional correlates. A reversal in the normal pattern of WM asymmetry of crossing fibers in patients may be consistent with an aberrant neurodevelopmental process.

Delineation of hippocampal subregions using T1-weighted magnetic resonance images at 3 Tesla.

Although several novel approaches for hippocampal subregion delineation have been developed, they need to be applied prospectively and may be limited by long scan times, the use of high field (>3T) imaging systems, and limited reliability metrics. Moreover, the majority of MR imaging data collected to date has employed a T1-weighted acquisition, creating a critical need for an approach that provides reliable hippocampal subregion segmentation using such a contrast. We present a highly reliable approach for the identification of six subregions comprising the hippocampal formation from MR images including the subiculum, dentate gyrus/cornu Ammonis 4 (DG/CA4), entorhinal cortex, fimbria, and anterior and posterior segments of cornu Ammonis 1-3 (CA1-3). MR images were obtained in the coronal plane using a standard 3D spoiled gradient sequence acquired on a GE 3T scanner through the whole head in approximately 10 min. The average ICC for inter-rater reliability across right and left volumetric regions-of-interest was 0.85 (range 0.71-0.98, median 0.86) and the average ICC for intra-rater reliability was 0.92 (range 0.66-0.99, median 0.97). The mean Dice index for inter-rater reliability across right and left hemisphere subregions was 0.75 (range 0.70-0.81, median 0.75) and the mean Dice index for intra-rater reliability was 0.85 (range 0.82-0.90, median 0.85). An investigation of hippocampal asymmetry revealed significantly greater right compared to left hemisphere volumes in the anterior segment of CA1-3 and in the subiculum.