Cutaneous receptive fields (RFs) of the fore- and hindpaw.

<p>Typical examples of cutaneous receptive fields (RFs) of neurons recorded in the fore- and hindpaw representation of a rat aged 4 months (A, upper panel) and a rat aged 30 months (B, lower panel). (A) RFs on the forepaw of young rats were very small (left) usually comprising only small parts of a digit or a single digit or pad. RFs on the hindpaw of young rats (right) were slightly larger than on the forepaw, typically consisting of a single digit or parts of a digit. On the more proximal area of the hindpaw, RFs comprised single pads and larger skin areas in the range of the heel. (B) RFs on the forepaw of old rats (left) were only slightly enlarged as compared to young animals. Typical RFs comprised parts of a digit or a single digit or pad. In contrast to the forepaw, RFs located on the hindpaw (right) of old rats were severalfold enlarged. RFs in old rats were characterized by representations of multiple digits and pads and by substantially enlarged RFs in the proximal parts of the paw.