Figure 1.

Multichannel unit recordings were performed in the prelimbic subregion of the medial prefrontal cortex of rats undergoing auditory fear conditioning and extinction. A, Rats were fear conditioned with tones of 30 s in length that coterminated with brief footshocks. Extinction training was conducted 2 h after conditioning, and the recall test occurred 24 h after extinction. B, Representative extracellular waveform sorting. The image shows superimposed waveforms of four simultaneously recorded neurons and the clusters they formed in three-dimensional space after applying principal component analysis. C, Coronal drawing shows location of recording electrodes [bregma +2.80 mm; adapted from Swanson (1992); ACd, dorsal anterior cingulate]. D, Percentage freezing to the tone (n = 17). Significant acquisition and extinction were observed on day 1, and substantial recall of extinction was observed on day 2. In this and subsequent figures, error bars illustrate SEM; Habit indicates habituation, and Cond indicates conditioning.