Location of auditory responsive neurons in the ventral PFC, below the principal sulcus (area 46), and anterior to the arcuate sulcus and area 8a, in areas 12 and 45. Left, macaque brain schematic indicating the recording cylinder (circle), the auditory responsive region in ventral PFC (blue grid) and the visual responsive region in the same animals (red grid). An enlargement of the auditory response grid at right shows the locations of auditory cells in the recording grid in x –y coordinates on the surface of ventral PFC (green circles, monkey 1; blue squares, monkey 2). Numbers on grid rows and columns correspond to medial–lateral and anterior–posterior coordinates where cells were located. 81% of the auditory cells were found within a 4 × 4 mm region (gray). Crosses (blue, monkey 1; green, monkey 2) correspond to locations of cells with auditory and visual responses (n = 5 cells). A total of 33 locations are shown (squares, circles and crosses) where 70 auditory cells were located. The locations of 10 cells (6 locations) that responded more strongly to vocalization than non-vocalization stimuli are portrayed by the circles and squares outlined in black. PCF, prefromtal cortex; IC, inferior convexity region; ls, lateral sulcus; los, lateral orbital sulcus; ps, principal sulcus; as acurate sulcus.

Prefrontal auditory neuron response profiles. Responses of 5 cells (a–e) to auditory stimuli are shown as raster (top panels) and post-stimulus time histograms (bottom panels). Gray bar below the histogram indicates onset and duration of auditory stimulus. Some sounds used are shown as waveforms below (e). Cell (a) gave a non-specific phasic onset response to all auditory stimuli tested, whereas auditory stimuli elicited a tonic response in cell (b) that lasted the length of the auditory stimuli. For some stimuli, cells (c, e) showed evidence of stimulus-synchronized activity (c, mv15; e, mv15). Whereas cells (a–c) responded to a variety of vocalization and non-vocalization stimuli, the responses of cells (d) and (e) were stronger for vocalizations compared to other complex stimuli, including white noise (d, witnos), and FM sweeps (e, swp5k). Whereas most PFC neurons responded to more than one auditory stimulus (66/70), cell (e) responded to only one stimulus, a vocalization (mv15) after testing with 32 complex stimuli. PSTH are calculated as spikes/s along the y-axis; bin width, 30 ms. All responses in (a–c) and the first 3 panels in (d) show a statistically significant increase (p < 0.05) over baseline responding in the inter-trial interval. For cell (e), only the response to mv15 was significant (p < 0.05). mv, monkey vocalization; hv, human vocalization (human vocalizations were spoken words); bp1-20K, band-passed noise range, 1–20 kHz; swp5k, FM sweep range 100–5,000 Hz.