Abstract
Getting older is associated with a decline of cognitive and sensorimotor abilities, but it remains elusive whether age-related changes are due to accumulating degenerational processes, rendering them largely irreversible, or whether they reflect plastic, adaptational and presumably compensatory changes. Using aged rats as a model we studied how aging affects neural processing in somatosensory cortex. By multi-unit recordings in the fore- and hindpaw cortical maps we compared the effects of aging on receptive field size and response latencies. While in aged animals response latencies of neurons of both cortical representations were lengthened by approximately the same amount, only RFs of hindpaw neurons showed severe expansion with only little changes of forepaw RFs. To obtain insight into parallel changes of walking behavior, we recorded footprints in young and old animals which revealed a general age-related impairment of walking. In addition we found evidence for a limb-specific deterioration of the hindlimbs that was not observed in the forelimbs. Our results show that age-related changes of somatosensory cortical neurons display a complex pattern of regional specificity and parameter-dependence indicating that aging acts rather selectively on cortical processing of sensory information. The fact that RFs of the fore- and hindpaws do not co-vary in aged animals argues against degenerational processes on a global scale. We therefore conclude that age-related alterations are composed of plastic-adaptive alterations in response to modified use and degenerational changes developing with age. As a consequence, age-related changes need not be irreversible but can be subject to amelioration through training and stimulation.
Highlights
Getting older is associated with a decline of cognitive and sensorimotor abilities
We have demonstrated that the functional organization of the hindpaw representation in somatosensory cortex of aged rats undergoes a significant deterioration: Receptive fields (RFs) of neurons recorded in the hindpaw representations of aged rats were enlarged, overlap between RFs was increased, and the topographic organization of cortical representational maps was broken down [10]
The walking pattern of young adult animals was characterized by prints where only the distal aspects of the digits, palms and pads were marked, indicative of a powerful way of moving without engaging the more proximal parts of the paws
Summary
Getting older is associated with a decline of cognitive and sensorimotor abilities. An increased life expectancy, combined with decreasing birth rates reverses the aging structure of industrialized countries with implications yet unforeseeable. The probability to suffer from age-related disorders rises dramatically, indicating an urgent need for increasing efforts towards a more comprehensive understanding of the different facets of aging [1,2]. Given this scenario, the preservation of every-day life competence of aged populations becomes increasingly important. Maintaining of sensorimotor abilities is a crucial prerequisite for a largely independent life In this context it is important to know whether age-related changes are due to the accumulation of degenerational processes and are largely irreversible, or whether they reflect plastic, adaptational and presumably compensatory changes
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