@article {183, title = {Selection of distinct populations of dentate granule cells in response to inputs as a mechanism for pattern separation in mice.}, journal = {Elife}, volume = {2}, year = {2013}, month = {2013}, pages = {e00312}, abstract = {

The hippocampus is critical for episodic memory and computational studies have predicted specific functions for each hippocampal subregion. Particularly, the dentate gyrus (DG) is hypothesized to perform pattern separation by forming distinct representations of similar inputs. How pattern separation is achieved by the DG remains largely unclear. By examining neuronal activities at a population level, we revealed that, unlike CA1 neuron populations, dentate granule cell (DGC) ensembles activated by learning were not preferentially reactivated by memory recall. Moreover, when mice encountered an environment to which they had not been previously exposed, a novel DGC population-rather than the previously activated DGC ensembles that responded to past events-was selected to represent the new environmental inputs. This selection of a novel responsive DGC population could be triggered by small changes in environmental inputs. Therefore, selecting distinct DGC populations to represent similar but not identical inputs is a mechanism for pattern separation. DOI:http://dx.doi.org/10.7554/eLife.00312.001.

}, keywords = {Animals, Behavior, Animal, Brain Mapping, CA1 Region, Hippocampal, Conditioning (Psychology), Cues, Dentate Gyrus, Environment, Fear, Gene Expression Regulation, Genes, Reporter, Memory, Memory, Episodic, Mental Recall, Mice, Inbred BALB C, Mice, Inbred C57BL, Mice, Transgenic, Neural Pathways, Neurons, Pattern Recognition, Physiological, Time Factors}, issn = {2050-084X}, doi = {10.7554/eLife.00312}, author = {Deng, Wei and Mayford, Mark and Gage, Fred H} } @article {196, title = {Collinear features impair visual detection by rats.}, journal = {J Vis}, volume = {11}, year = {2011}, month = {2011}, abstract = {

We measure rats{\textquoteright} ability to detect an oriented visual target grating located between two flanking stimuli ("flankers"). Flankers varied in contrast, orientation, angular position, and sign. Rats are impaired at detecting visual targets with collinear flankers, compared to configurations where flankers differ from the target in orientation or angular position. In particular, rats are more likely to miss the target when flankers are collinear. The same impairment is found even when the flanker luminance was sign-reversed relative to the target. These findings suggest that contour alignment alters visual processing in rats, despite their lack of orientation columns in the visual cortex. This is the first report that the arrangement of visual features relative to each other affects visual behavior in rats. To provide a conceptual framework for our findings, we relate our stimuli to a contrast normalization model of early visual processing. We suggest a pattern-sensitive generalization of the model that could account for a collinear deficit. These experiments were performed using a novel method for automated high-throughput training and testing of visual behavior in rodents.

}, keywords = {Animals, Behavior, Animal, Conditioning (Psychology), Contrast Sensitivity, Lighting, Orientation, Photic Stimulation, Psychophysics, Rats, Retina, Space Perception}, issn = {1534-7362}, doi = {10.1167/11.3.22}, author = {Meier, Philip and Flister, Erik and Reinagel, Pamela} } @article {195, title = {Rat performance on visual detection task modeled with divisive normalization and adaptive decision thresholds.}, journal = {J Vis}, volume = {11}, year = {2011}, month = {2011}, abstract = {

Performance on any perceptual task depends on both the perceptual capacity and the decision strategy of the subject. We provide a model to fit both aspects and apply it to data from rats performing a detection task. When rats must detect a faint visual target, the presence of other nearby stimuli ("flankers") increases the difficulty of the task. In this study, we consider two specific factors. First, flankers could diminish the sensory response to the target via spatial contrast normalization in early visual processing. Second, rats may treat the sensory signal caused by the flankers as if it belonged to the target. We call this source confusion, which may be sensory, cognitive, or both. We account for contrast normalization and source confusion by fitting model parameters to the likelihood of the observed behavioral data. We test multiple combinations of target and flanker contrasts using a yes/no detection task. Contrast normalization was crucial to explain the rats{\textquoteright} flanker-induced detection impairment. By adding a decision variable to the contrast normalization framework, our model provides a new tool to assess differences in visual or cognitive brain function between normal and abnormal rodents.

}, keywords = {Adaptation, Physiological, Animals, Choice Behavior, Cognition, Conditioning (Psychology), Contrast Sensitivity, Male, Models, Neurological, Photic Stimulation, Psychomotor Performance, Rats, Rats, Long-Evans, Visual Perception}, issn = {1534-7362}, doi = {10.1167/11.9.1}, author = {Meier, Philip and Reinagel, Pamela} }