Our research program aims to determine the neural basis for spatial
cognition, decision-making, and episodic memory. Recent projects have
focused primarily on examination of multiple single-unit recordings made
in freely behaving animals. Our most recent work concerns recordings
made in the parietal cortex, hippocampus, subiculum, and premotor cortex
in rats performing either a multiple-T working memory task or executing
traversals of differently shaped spiral paths. One new project will
examine the activity patterns of basal forebrain neurons during
performance of a task demanding dynamic allocation of attentional
Databyte - Hippocampus
Databyte - Parietal Cortex
Databyte - Basal Forebrain
Center plot shows the color-mapped firing rate of 600 basal forebrain neurons categorized according to their times of peak activity across the stages of a selective attention task. Surrounding plots show the color-mapped firing rates of individual neurons across multiple trials, highlighting the reliability of task-phase specific activity and heterogeneity, across neurons, of such activity. Category 1 neurons responded to light stimuli. Category 4 neurons during movement to the attended light source. Category 15 neurons fire most during nosepoke at the light source. Category 17 neurons are reward responsive. The data suggest that the basal forebrain coordinates shifts in attention appropriate to each task phase.
Databyte - Subiculum
Positional firing ratemaps for a subiculum 'axis-tuned' neuron as the animal traversed multiple routes within a complex set of interconnected pathways. The path network was rotated 90 degrees to determine whether firing patterns were spatially organized by the reference frame of the recording room (not shown) or the reference frame of the path network. To the right are polar firing rate plots that describe the firing rate of the same neuron according to the head orientation of the animal relative to the recording room. Under both the normal (upper plots) and rotated (lower plots) configurations of the path network, the neuron fires whenever the animal travels east OR west, thus exhibiting specificity to movement along the east/west axis. Such 'axis-tuning' is organized relative to the space of the larger environment (the recording room) since the positional firing rate map changes upon rotation but the polar firing rate map does not. Neurons such as these effectively encode the possible directions of travel associated with any given track location as well as the orientations of all pathways relative to the environment.
Databyte - Retrosplenial Cortex
Retrosplenial cortex and hippocampal CA1 neurons were recorded as animals circumnavigated a plus-shaped pathway. In these panels the positional firing rates of retrosplenial neurons (left) and CA1 neurons (center) are color-mapped (low-white, high-black). Each neuron's positional rate vector for the full run (x-axis) has been rotated to the 'point of symmetry' on the maze where the firing pattern over the preceding and subsequent halves of the track are the most similar. Retrosplenial populations exhibit recursion in patterning for all distances from the point of symmetry (center of x-axis). Such patterning is much weaker for CA1 neuron populations. The result indicates that retrosplenial populations effectively generate a map of distance from any given track location of the animal to ALL other track locations.