Comparison of response ratio among four groups. A–D, Percentages of MGB units showing response ratios (SEQ/RAN) to SAM stimuli set in young anesthetized (A, YoungAnes), young awake (B, Young), aged anesthetized (C, AgedAnes), and aged awake (D, Aged) rats. The percentage of units showing a preference for SEQ SAM stimuli increased from young anesthetized rats (7%, 3 of 42) to young awake rats (16%, 12 of 73) and then aged awake rats (30%, 18 of 60). Aged awake rats showed the highest percentage of SEQ-preferring units, while none of the units from aged anesthetized rats shows SEQ preference. χ2 Test indicates significant portion differences (x(2)2 = 25.15, p < 0.0001) between the anesthetized group (YoungAnes) and unaesthetized group (Young). There was a significant, p < 0.05 (x(2)2 = 8.934, χ2 test) difference between young and aged awake groups.