Value-based decision-making operates on multiple variables-including offer value, choice, expected outcome, and recent history-each functioning at different times in the decision process. Orbitofrontal cortex (OFC) has long been implicated in value-based decision-making, but it is unclear how downstream circuits might read out complex OFC responses into separate representations of the relevant variables to support different cognitive functions at specific times. We recorded from single neurons in OFC while macaque monkeys made cost-benefit decisions to juice offers. Using a novel analysis-optimal targeted dimensionality reduction-we discovered orthogonal, static dimensions (i.e. linear combinations of neurons) that selectively represented the value, choice, and expected reward of the present and, separately, previous offers. The neural composition of most representations was stable over discrete time periods that aligned to concurrent cognitive demands. We applied a new set of statistical methods to determine that the sensitivity, specificity and stability of the representations were greater than expected from the low-level features-dimensionality and temporal smoothness-of the responses alone. The separability and stability of OFC representations suggest a mechanism by which downstream circuits can read out specific task-relevant variables at appropriate times. Kimmel et al., 12/31/19 OFC Value and Choice Representations p. 2 of 103where 0 ≤ ≤ 1 specified the maximal accept rate, or saturation point of the psychometric curve. This parameter has previously been used to model the lapse rate, or intrinsic failure rate, of behavior 26 . The exponent took the form:where 3 was a constant and + determined the influence of the offered benefit [0, 1, 2, 4, 8] on trial t raised to , an exponent typical in economic models to implement a non-linear utility function 27 that was either fixed ( = 1) or allowed to vary as a free parameter. The benefit predictor was scaled to the range [0, 1].
Anatomy
Supplementary Figure 4. MRI localization.Anatomical MRI sequences were acquired with recording grid in place prior to physiological recording. (a,b) T2-or T1-weighted coronal slice is shown at the median anterior-posterior extent of recorded sites for monkey N (a) or K (b), respectively. Animal's right side is shown on the left side of the image, per radiological convention. The inset shows an axial slice through the recording grid (white horizontal arrow), with a representative grid hole circled corresponding to grid position 2A or 0G (43.1 or 36.6 mm anterior to the interaural line, measured via intra-surgical stereotaxic coordinates; 6.7 or 6.3 mm left of midline, measured from the post-surgical MRI) for monkey N or K, respectively (see Supplementary Figure 7). Recording grid was filled with salinized agarose solution to facilitate contrast on MRI. By registering the axial slice through the recording grid and the coronal slice containing the selected grid position, we traced the virtual electrode trajectory from the bottom of...