Fig. 5. FBN rat layer V neurons exhibit two major types of receptive field maps. (A) 32% showed the classic V/U-shape with young and aged neurons showing similar responses to current pulse stimulation (not shown). (B) 47% of pyramidal neurons demonstrated a more complex, dynamic response map. (C) Aged complex receptive field neurons responded more vigorously than young neurons to 200 ms current pulses, suggesting altered inhibitory control. Such increased excitability to current would be consistent with reduced GAD₆₇ immunostaining around layer V (LV) somata (see insets; scale bars, 5 µm). (Modified from Turner et al., 2005c.)