Background
Stroke is the most common cause for adult disability and the third most common for death in North America. It occurs from interruptions in the blood supply to the brain, which induces a sudden disabling attack or loss of consciousness. On a cellular level, neurons and other types of cells become deprived of oxygen and begin to show signs of structural damage in as little as two minutes. While oxygen deprived, other physiological processes begin to decline due to chemical imbalances and ultimately result in apoptosis, or cell death. As apoptotic events occur, sensory and motor functions become impaired, which may result in permanent damage. Although the initial stroke event is traumatic, a majority of patients will survive. Specifically, approximately 795,000 patients suffer a stroke per year with an 82% survival rate in the United States. After the initial stroke event, the brain will undergo some spontaneous recovery, which can be further improved with rehabilitation.
Some current rehabilitation treatments are tested in mice. A majority of these tests are focused on motor and sensorimotor function, since human stroke often results in impaired limb function. Functions of interest include coordination and balance (rotarod), sensory asymmetry (adhesive tape removal test), forepaw function (cylinder test, forelimb placing, reaching tasks, staircase test) and hindlimb function (foot fault test, ledged tapered beam). Typically, a lesion is induced in the area of the mouse brain that affects a specific motor function, such as paw behavior. Studying motor function pre-stroke, post-stroke, and after treatment gives an indication of the effectiveness of that treatment on stroke recovery.
Whisker sensorimotor behavior has become an area of interest in the field, as approximately 70% of the primary somatosensory cortex of rodents is devoted to sensing input from whiskers. Given that the majority of this cortex relies on whisker sensing, measurements involving whisker function have the potential to become the gold standard for mouse stroke studies. Current whisker motion tests involve training mice to perform tasks and assessing whisker movement. These performance tests introduce additional variables that may skew results and also require training time. There are many non-whisker behavior tests, such as those mentioned above, which do not require training and are more commonly used in the field for their greater reliability and shorter procedure time. Thus, an accurate whisker sensorimotor behavior test for untrained mice could potentially transform the way stroke studies are currently researched.