Failure of induced asymmetries to improve left-right response differentiation in the rat.

Rats (and humans) appear to be able to distinguish between left and right by referring to an intrinsic asymmetry as a navigational aid; this suggests that experimentally induced asymmetries might also facilitate such a distinction. We assessed the effects of asymmetries produced by unilateral shaving, unilateral vibrissotomy, and asymmetrical cortical lesions on acquisition of a left-right response differentiation. None of the treatments improved performance relative to appropriate control treatments; the rats were evidently unable to use these induced asymmetries to form the lateral differentiation. The results are related to evidence provided in an earlier report (Noonan & Axelrod, 1989) that even some reliable intrinsic asymmetries cannot function as navigational aids.