Biomedical subjects

Patricia E Sharp

Publications and source records attributed to Patricia E Sharp.

4 recordsLinked to original sources

PubMed2006

Subicular place cells generate the same "map" for different environments: comparison with hippocampal cells.

Since the initial discovery of place cells in the hippocampus proper, similar spatial firing has been observed in additional regions throughout the hippocampal formation. One such region is the subiculum. Here, most cells show a significant, consistent variation in rate relative to location. Thus, subicular and hippocampal cells are similar, in providing a representation of momentary location in space. However, there are also some fundamental differences. First, many subicular cells have a directional signal superimposed on the place-related patterns. In contrast, hippocampal cells in the open field paradigm used here typically do not show a genuine directional component. The second critical difference has to do with how the cells code different environments. As is well known, hippocampal cells show different spatial patterns in environments which offer distinctly different stimulus properties. For example, a hippocampal cell which fires in the northwest portion of a striped cylinder will likely display a different field, or no field, when recorded in a gray square. In contrast, subicular cells are likely to show the same behavior across environments, such as choosing the northwest region of both enclosures. Further, if two environments differ in size, the subicular patterns will expand/shrink to fit. Thus, it appears that subicular cells form a rigid framework of interrelated firing fields which is fit into each new enclosure. In contrast, hippocampal cells create a new "map" specific to each environment. This suggests that the hippocampal and subicular regions work together to help provide the overall cognitive mapping abilities of the animal.

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PubMed2006

Neuronal implementation of hippocampal-mediated spatial behavior: a comparative evolutionary perspective.

The hippocampal formation (HF) of mammals and birds plays a strikingly similar role in the representation of space. This evolutionarily conserved property, however, belies the contrasting spatial ecology of animals such as rats and homing pigeons, differing spatial ecologies that should have promoted the evolution of group-specific adaptations to the HF representation of space. However, the spatial response properties of pigeon and rat HF neurons reveal surprising similarity in the contribution of position, direction, and trajectory toward explaining spatial variation in firing rate. By contrast, the asymmetrical distribution of neuronal response properties in the left and right HF of homing pigeons, but not rats, indicates a difference in network organization. The authors propose that hippocampal evolution may be characterized by inertia with respect to changes in the basic spatial elements that determine the response properties of neurons but considerable plasticity in how the neuronal response elements are organized into functional networks.

Animals↗

PubMed2005

Movement-related correlates of single cell activity in the interpeduncular nucleus and habenula of the rat during a pellet-chasing task.

The habenula and interpeduncular nucleus (IPN) are part of a dorsal diencephalic conduction system which receives input from cholinergic, striatal, and hypothalamic areas, and sends output to several, disparate midbrain regions. These output regions include the dorsal tegmental nucleus, which is part of a navigation-related system that provides a signal for directional heading. The habenula and IPN also project to the dorsal and medial Raphe nuclei, thought to be involved in mood and behavioral state regulation. Here, cells in both the habenula and IPN were recorded in freely moving rats while they foraged for food pellets. There were four major findings. First, many of the cells tended to fire in sporadic bouts of relatively high versus low rates, and this may be related to intrinsic cell properties discovered during in vitro studies. Second, although these regions are connected to the direction signaling circuit, they do not, themselves demonstrate a directional signal. Third, about 10% of the cells in the lateral habenula showed a strong correlation between rate and angular head motion. This may constitute an important, requisite input to the above-mentioned head direction circuit. Finally, many of the cells in each region showed a temporally coarse correlation with running speed, so that bouts of high frequency firing coincided with episodes of higher behavioral activation. This last finding may be related to work which shows an influence of the habenula on locomotor activity, and in relation to the protective effects of exercise in relation to stress, as mediated by the Raphe nuclei.

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PubMed2005

Movement-related correlates of single-cell activity in the medial mammillary nucleus of the rat during a pellet-chasing task.

Although the functional role of the mammillary bodies has remained obscure, lesion studies suggest this structure may play a role in memory-in particular, memory for spatial information. Indeed, anatomically, the mammillary bodies are strongly interconnected with limbic system regions, such as the hipppocampal formation, which are also thought to play a role in spatial behavior. Each of these limbic regions so far investigated contains cells that signal either the momentary location and/or directional heading of an animal as it travels through space. In fact, the lateral mammillary nucleus itself contains head direction cells, and is thought to be critical for the initial calculation of this directional signal. Here, we provide an initial report on cell activity in the medial mammillary nucleus. Cells were recorded while rats performed a pellet-chasing task that has been used for much of the work on place and head direction cells. The main findings are 1) approximately 1/3 of the cells showed a temporally precise relationship to angular motion of the head, so that they differentially indicated clockwise versus counterclockwise angular motion, 2) approximately 60% of the cells showed a temporally coarse correlation with translational motion, 3) firing rate for almost all cells was strongly modulated at theta frequency, and 4) no cells showed evidence of either directional or place-related activity. These data suggest that the medial and lateral mammillary nuclei together provide the directional and trajectory information thought to be critical for generation of the spatial signals in the hippocampal region.

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