Abstract
Alzheimer's disease (AD) is caused by progressive changes in neural circuits that culminate in memory
loss, confusion, difficulty completing tasks, withdrawal, mood changes and ultimately death. Alterations in body
movement — such as slowed gait, and difficulty in avoiding obstacles — have been associated with AD, are
predictive of AD, and often appear in the pre-clinical stage, before cognitive changes are apparent. These
observations raise important questions about how AD targets the cognitive and motor systems that support
movement and/or action selection; addressing these questions in turn requires a clear view of how AD
pathophysiology influences behavior both early and late in disease, and particularly how these changes in
behavior are distinguished from the many motor-related changes apparent during normal aging. However, to
date behavioral analysis of movement in AD mouse models have not yet yielded a clear and consistent view of
how AD affects the neural circuits responsible for selecting, composing, sequencing and implementing ongoing
behaviors. At least in part this failure reflects the methods used to characterize behavior in mouse models,
which depend upon a set of reductionist assays that capture limited aspects of a mouse's overall behavioral
comportment within a given experiment; as a consequence we do not know whether different AD models share
core movement phenotypes, nor do we understand whether or how AD targets the cortico-striatal circuits that
create the coherent, moment-to-moment patterns of action used by mice to interact with the world. Our
laboratory has recently developed a novel behavioral characterization technique, based upon 3D machine
vision and unsupervised machine learning techniques, called Motion Sequencing (MoSeq). MoSeq
automatically and without human supervision identifies the behavioral modules (“syllables” e.g., a left turn, the
first half of a rear, etc.) out of which spontaneous and self-directed behavior is composed, as well as the
statistical rules governing the sequencing of these syllables (“grammar”). We have previously demonstrated
that the dorsolateral striatum (DLS) contains explicit neural correlates for both syllables and grammar, and that
the DLS is causally required to assemble syllables into meaningful and adaptive sequences. Here we propose
to use MoSeq to characterize behavioral phenotypes expressed by a variety of AD mouse models, to perform
joint neural-behavioral recordings to probe circuit mechanisms that underlie these observed phenotypes and,
finally, to develop MoSeq into a broadly-applicable platform for studying the movement-related signatures of
cognition. Taken together, these experiments promise to revitalize the study of behavior and neuro-behavioral
relationships in pre-clinical models of AD, and to reveal key mechanisms that tie together AD-related genetic
lesions, neural circuit function, and ongoing naturalistic patterns of action.