Abnormal tactile experience early in life disrupts active touch.

The importance of early tactile experience in the development of discriminative somatomotor function was assessed by examining the proficiency and movement strategies of rats raised without normal sensory inputs provided by their mystacial vibrissae. Infant-trimmed animals had their whiskers clipped daily from birth to 45 d of age, after which they were allowed to regrow for 60-70 d before initiation of behavioral training, which lasted as long as several months. Adult-trimmed animals had their whiskers trimmed for comparable periods during adulthood. Rats were tested on one of two tactile discriminations, rough versus smooth or rough versus rough, that differed with respect to the overall size of their surface features. Whisker movements during task performance were examined in detail using video-based motion analysis software. Infant-trimmed animals performed rough versus smooth discriminations as well as adult-trimmed rats or normally reared animals. Except for one subject, infant-trimmed rats were severely impaired in their ability to distinguish rough versus rough surfaces. Deficits persisted in spite of months of training with the regrown vibrissae. The animals that failed to master this task displayed whisking patterns that notably lacked frequencies in the normal range of 6-12 Hz. Thus, abnormal tactile experience early in life substantially, and perhaps permanently, impairs sensorimotor integration underlying active touch.