Philip A. Blankenship

Otolithic Information is Required for Homing in the Mouse

Navigation and the underlying brain signals are influenced by various allothetic and idiothetic cues, depending on environmental conditions and task demands. Visual landmarks typically control navigation in familiar environments but, in the absence of landmarks, self‐movement cues are able to guide navigation relatively accurately. These self‐movement cues include signals from the vestibular system, and may originate in the semicircular canals or otolith organs. Here, we tested the otolithic contribution to navigation on a food‐hoarding task in darkness and in light. The dark test prevented the use of visual cues and thus favored the use of self‐movement information, whereas the light test allowed the use of both visual and non‐visual cues. In darkness, tilted mice made shorter‐duration stops during the outward journey, and made more circuitous homeward journeys than control mice; heading error, trip duration, and peak error were greater for tilted mice than for controls. In light, tilted mice also showed more circuitous homeward trips, but appeared to correct for errors during the journey; heading error, trip duration, and peak error were similar between groups. These results suggest that signals from the otolith organs are necessary for accurate homing performance in mice, with the greatest contribution in non‐visual environments.

Otolith dysfunction alters exploratory movement in mice

Abstract The organization of rodent exploratory behavior appears to depend on self‐movement cue processing. As of yet, however, no studies have directly examined the vestibular system’s contribution to the organization of exploratory movement. The current study sequentially segmented open field behavior into progressions and stops in order to characterize differences in movement organization between control and otoconia‐deficient tilted mice under conditions with and without access to visual cues. Under completely dark conditions, tilted mice exhibited similar distance traveled and stop times overall, but had significantly more circuitous progressions, larger changes in heading between progressions, and less stable clustering of home bases, relative to control mice. In light conditions, control and tilted mice were similar on all measures except for the change in heading between progressions. This pattern of results is consistent with otoconia‐deficient tilted mice using visual cues to compensate for impaired self‐movement cue processing. This work provides the first empirical evidence that signals from the otolithic organs mediate the organization of exploratory behavior, based on a novel assessment of spatial orientation.

Cholinergic deafferentation of the hippocampus causes non-temporally graded retrograde amnesia in an odor discrimination task

Dementia of the Alzheimers type (DAT) is a neurodegenerative disorder marked by loss of hippocampal cholinergic tone and significant memory impairments, specifically for memories acquired prior to disease onset. The nature of this relationship, however, remains debated. The current study used the string pulling task to evaluate the temporal effects of odor discrimination learning in animals with selective cholinergic lesions to determine the role of the septohippocampal cholinergic system in mnemonic function. Rats with 192-IgG-Saporin lesions to the medial septum had a higher number of correct responses in the reversal training when compared to sham rats, suggesting an inability to retrieve the previously learned discrimination; however, no temporal gradient was observed. Furthermore, there were no group differences when learning a novel odor discrimination, demonstrating the ability for all rats to form new memories. These results establish a role for the cholinergic medial septum projections in long-term memory retrieval. The current study provides a behavioral assessment technique to investigate factors that influence mnemonic deficits associated with rodent models of DAT.

A history of adolescent binge drinking in humans is associated with impaired self-movement cue processing on manipulatory scale navigation tasks

A binge drinking pattern of alcohol consumption has been shown to have an impact on brain structures that continue to develop into late adolescence. These same brain structures have been implicated in processing self-movement cues. The current study applies an array of existing and novel kinematic analysis techniques to characterize performance on manipulatory scale tasks to assess spatial orientation deficits associated with a history of adolescent binge drinking. Using kinematic analysis techniques, a history of adolescent binge drinking in university students was associated with disruptions in outward segment movement organization and less accurate direction and distance estimation in a dead reckoning task. Similar disruptions in performance were found in the bead maze task in the first training block; however, no group differences were observed on subsequent blocks of place training. This is the first study to demonstrate a relationship between adolescent binge drinking in humans and impaired processing of self-movement cues. This pattern of results demonstrates the potential of manipulatory-scale spatial tasks to detect differences in information processing associated with factors known to disrupt normal central nervous system development.

The medial frontal cortex contributes to but does not organize rat exploratory behavior.

Animals use multiple strategies to maintain spatial orientation. Dead reckoning is a form of spatial navigation that depends on self-movement cue processing. During dead reckoning, the generation of self-movement cues from a starting position to an animals current position allow for the estimation of direction and distance to the position movement originated. A network of brain structures has been implicated in dead reckoning. Recent work has provided evidence that the medial frontal cortex may contribute to dead reckoning in this network of brain structures. The current study investigated the organization of rat exploratory behavior subsequent to medial frontal cortex aspiration lesions under light and dark conditions. Disruptions in exploratory behavior associated with medial frontal lesions were consistent with impaired motor coordination, response inhibition, or egocentric reference frame. These processes are necessary for spatial orientation; however, they are not sufficient for self-movement cue processing. Therefore it is possible that the medial frontal cortex provides processing resources that support dead reckoning in other brain structures but does not of itself compute the kinematic details of dead reckoning.

Unilateral lesions of the dorsocentral striatum (DCS) disrupt spatial and temporal characteristics of food protection behavior.

Spatial and temporal information processing provide a foundation for higher cognitive functions. The survival of animals depends on integrating spatial and temporal information to organize behavior. In general, previous research has focused on only one source of information processing; however, there is evidence to support a convergence in the processing of egocentric-spatial and temporal information within a cortico-striatal system of structures. The current study evaluated the contributions of the dorsocentral striatum (DCS) to egocentric-spatial and temporal (within the seconds-to-minutes range) processing of information using a food protection task. Long-Evans rats received unilateral NMDA lesions of the DCS followed by testing in a food protection task. Performance in this task is mediated by the motivation of the animal to consume a food item, their perception of the time required to consume a food item, their sensory ability to process egocentric cues, and their motor ability to evade an incoming conspecific. Unilateral DCS lesions were shown to impact both spatial and temporal characteristics of food protection. These results suggest that the DCS may be a critical structure for the integration of egocentric-spatial and temporal information within the interval timing range.