Executive control: The ability to coordinate thought and action by directing them toward goals. Monkey Human The prefrontal cortex Our approach: Multiple-electrode recording in trained monkeys. This allows detailed comparisons between neuron populations that are not confounded by extraneous factors (e.g., behavioral performance, training, level of experience, etc.), especially the timing of neural activity. 1 1

Model-Building in the Prefrontal Cortex: “Cats” Versus “Dogs” Category boundary Prototypes 100% Cat 80% Cat Morphs 60% Cat 60% Dog 80% Dog 100% Dog Learned categories: monkeys had no prior experience with cats and dogs and could learn to categorize the stimuli after their reassignment to arbitrary categories. 2 2

About 1/3 of Randomly-Selected Prefrontal Neurons Respond to Category Membership not Physical Appearance Activity to individual stimuli along the 9 morph lines that crossed the category boundary Single neuron: C1 C2 C3 D1 D2 D3 “cats” “dogs” category boundary C1 C2 C3 D2 D3 D1 0.5 1.0 Normalized firing rate Freedman, Riesenhuber, Poggio, and Miller (2001) Science Freedman, Riesenhuber, Poggio, and Miller (2002) J. Neurophysiology Freedman, Riesenhuber, Poggio, and Miller (2003) J. Neuroscience 3 3

Are Prefrontal Neurons Category Multi-taskers? We trained monkeys to categorize the same images under two different category schemes

Are Prefrontal Neurons Category Multi-taskers? Many individual PFC neurons are only reflected one category distinction (and only when it was relevant).

Are Prefrontal Neurons Category Multi-taskers? Next, we trained monkeys on two independent (non-competing) category distinctions.

Are Prefrontal Neurons Category Multi-taskers? More individual PFC neurons reflected both category distinctions.

Category Representations in the PFC are Highly Dependent on Task Demands More overlap in neural representations when they are independent… …then when they are related and competing. Note: If PFC representations depended more on bottom-up (sensory) information, there should be more overlap for the related category sets because they use the same stimuli.

How Do “Top-Down” Signals Flow Across the Cortex? New Project: How Do “Top-Down” Signals Flow Across the Cortex? MT LIP PFC ITC

Tracing the Flow of Signals Using Neural Synchrony MT LIP PFC ITC Tracing the Flow of Signals Using Neural Synchrony The directed information flow was quantified as the baseline-corrected asymmetry of the generalized partial directed coherence (GPDC) derived from a sliding window multivariate autoregression.