Fear conditioning and brain activity: A positron emission tomography studyin humans

Regional cerebral blood flow (rCBF) was measured with (H2O)-O-15 positron e mission tomography in 8 healthy women before and after fear conditioning (i .e., paired shocks) and unpaired shocks to videotape cues. Conditioning was supported by enhanced peripheral nervous system recordings and subjective ratings. Fear conditioning increased rCBF in the central gray of the midbra in; bilaterally in the hypothalamus, the thalamus, and the left striatum; a nd in the right and left anterior cingulate and right prefrontal cortices. Regional CBF was attenuated bilaterally in the right and left prefrontal, t emporal (including the amygdala), parietal, and occipital cortices, and in the left orbitofrontal cortex. When compared with unpaired shock presentati ons, fear conditioning resulted in elevated rCBF in the left cerebellum. He nce, in the present paradigm, only neural activity in the left cerebellum s olely reflected processes associated with true Pavlovian conditioning.