More about Miller Lab Research
Miller Lab research aims to understand how the prefrontal cortex, a neural system located in the frontal lobe of the brain, subserves cognitive control. Cognitive or executive control involves the higher-order processing that comes into play when our behavior has to be guided by plans, thoughts, and goals. This sort of behavior contrasts with the one that is primarily driven by external stimuli or by emotion, as well as with behavior that is stereotypical and automatic. Although the prefrontal cortex (PFC) has long been thought to mediate executive functions in the human brain, the mechanisms through which PFC regulates this goal-oriented, purposeful behavior were not clearly understood.
Research conducted in Earl Miller’s laboratory has shown that such cognitive control is manifested in the neural activity in the primate PFC. The activation of PFC neurons reflect the abstract cognitive process that guides behavior during a control-demanding task. PFC neurons, thus, have been documented to represent top-down information such as abstract rules like “same vs. different”, to process the category or quantity of visual stimuli, and to guide the allocation of attentional resources. PFC activity has also been shown to reflect the flexible remapping of stimulus-response associations. These results have arisen through a combination of electrophysiological, psychophysical, and computational techniques. Another contribution is demonstrating that many cortical neurons are multifunctional (i.e., show “mixed selectivity”). This has been a major advance beyond earlier theories that posited that each neuron has a specific function. This property gives the brain greater computational horsepower and endows flexibility, a hallmark of higher-level cognition.
Miller Lab has innovated techniques for recording from many neurons simultaneously in multiple brain areas. This is a departure from the classic single-neuron recording approach. It allows the examination of the emergent properties of networks of neurons. Miller’s lab has used this approach to make a number of discoveries of how different brain areas collaborate to produce thought and action. This includes recent discoveries that oscillating “brain waves” may control the timing of shifts of attention and that different thoughts simultaneously held in working memory line up on different phases of each brain wave. The latter may explain why we can only think about a few things at the same time.
The Miller Lab has also mounted evidence for an update to the oldest and most fundamental neural model of cognition: Working memory. For the past 50 years, working memory has been thought to rely on cortical neurons that fire continuous impulses that keep thoughts “online”. Work from the Miller lab has revealed more complex dynamics. The impulses fire sparsely and interact with brain waves of different frequencies. Higher frequency brain waves carry the contents of working memory while lower frequency brain waves act as control signals that gate access to and clear out working memory. They have recently demonstrated that the same dynamics under Predictive Coding, the brain’s ability to automatically generate predictions about forthcoming sensory inputs. Predictive Coding is how the brain prevents sensory overload. Its dysfunction may explain autism.
Miller’s paper with Jonathan Cohen, An Integrative Theory of Prefrontal Cortex Function, has been designated a Current Classic as among the most cited papers in Neuroscience and Behavior. It is the 5th most-cited paper in the history of Neuroscience. His paper with Tim Buschman, Top-down versus Bottom-up Control of Attention in the Prefrontal and Posterior Parietal Cortices was The Scientist‘s Hot Paper for October 2009.