Monkey

Human

The prefrontal cortex

Executive control:

The ability to coordinate thought and action by directing them toward goals.

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.

Category boundary

Prototypes

100% Cat

80% Cat Morphs

60% Cat Morphs

60% Dog Morphs 80% Dog

Morphs

Prototypes 100% Dog

Model-Building in the Prefrontal Cortex: “Cats” Versus “Dogs”

Learned categories: monkeys had no prior experience with cats and dogs and could learn to categorize the stimuli after their reassignment to arbitrary categories.

“cats”

“dogs”

category boundary

C1

C2

C3

D2

D3D1

Activity to individual stimuli along the 9 morph lines that crossed the category boundary

Single neuron:

0 0.5 1.0

Normalized firing rate

C1C1C1C2C2C2

C3C3

C3

D1D2D3D1D2D3

D2D3

D1

About 1/3 of Randomly-Selected Prefrontal Neurons Respond to Category Membership not Physical Appearance

Freedman, Riesenhuber, Poggio, and Miller (2001) ScienceFreedman, Riesenhuber, Poggio, and Miller (2002) J. NeurophysiologyFreedman, Riesenhuber, Poggio, and Miller (2003) J. Neuroscience

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

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.

More overlap in neural representations when they are independent…

…then when they are related and competing.

MTLIP

PFC

ITC

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

MTLIP

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.