One horse walks circles compulsively and appears as if he hasn’t had his morning coffee. Another stands a bit lopsided and doesn’t blink when you raise your hand toward her eye. The bad news is both horses show signs of potential neurologic disease, and their veterinarians are tasked with digging deep, remembering which sections of the nervous system control which body parts, and whether the function is same-side or mirrored. The good news is horses give very subtle clues that can help the clinician pinpoint the cause so treatment can start.

Robert MacKay, BVSC, PhD, Dipl. ACVIM, professor of Large Animal Clinical Sciences at the University of Florida College of Veterinary Science, described the possible meaning of some confusing neurologic findings the 2015 American Association of Equine Practitioners (AAEP) Convention, held Dec. 5-9, in Las Vegas.

Consciousness

MacKay began by describing the life-sustaining operation of consciousness, which is based in the reticular formation of the brain and runs the cardiovascular system, breathing, and swallowing. A part of this formation, called the ascending reticular activating system (ARAS), is responsible for wakefulness and transitions in and out of wakefulness. Injury location determines the effect on a horse’s wakefulness. For instance, midbrain injury (to the uppermost part of the brainstem, which is involved in basic, unconscious body function) results in profound obtundation, or dulled alertness; cerebral injury (the portion of the brain concerned with conscious thought, perceptions, and learned skills) might have no effect at all to a serious effect on consciousness; and widespread injury to the forebrain, which, as it sounds, is the forward-most part of the vertebrate brain, including the cerebrum, hypothalamus, and thalamus, is necessary to moderately affect consciousness.

Behavioral Changes

Changes in a horse’s behavior can also be explained by brain injury location. For instance, says MacKay, a horse with dementia is likely to have a forebrain lesion