We examined theta activity in the temporal hippocampus of ure-thane-chloralose-anesthetized pigs by stimulation with two chemical odors, beta-phenyl ethyl alcohol (PEA; rose-like odor) and n-amyl acetate (banana-like odor). Neural activity was recorded in the neural cell layer nearby fimbria of the temporal hippocampus in three of six animals. Odor stimulation with PEA at a low concentration (10-4 w/w; 100 ppm) significantly increased power of the low-frequency theta band (type-2; 4 - 6 Hz) for the middle 10 s (w (3, 6, 2.5%) >2.56). The PEA odor at a higher concentration (10-3 w/w; 1000 ppm), however, showed a tendency for gradual increase in？the low-frequency theta but the response was insignificant compared with the control. On the other hand, odor stimulation with n-amyl acetate (10-4 w/w; 100 ppm) caused no apparent increase or a tendency for decrease in power of the low-frequency theta. Thus, the type-2 theta response in the temporal hippocampus to the PEA odor contrasted strikingly with that to the n-amylacetate in the ure-thane-chloralose-anesthetized pigs. The response of the type-2 theta rhythm in the temporal hippocampus may underlie the difference in emotional sensation and cognition of PEA from n-amyl acetate in the pig.
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