Our lab studies several neocortical contributions to episodic memory and decision-making using a variety of techniques such as electroencephalography (EEG), functional magnetic resonance Imaging (fMRI), transcranial direct-current stimulation (tDCS), transcranial magnetic stimulation (TMS), and patient studies. These studies range from investigations into prefrontal and parietal cortex activity associated with shifts in decision criteria to attempts to uncover the sources variability of individual patterns of brain activity during an episodic memory task. Ultimately, our goal is to use these neuroscientific studies to understand the processes of the mind when remembering a past event or making a decision, and to appreciate the uniqueness of these processes at the individual level.

Criterion Shifting in Recognition Memory

Miller Lab Criterion Shifting Research

A critical aspect of recognition memory involves weighing the strength of memory evidence against a decision criterion. The placement of a decision criterion is affected by several factors, such as the probability of a target or the varying consequences of a miss versus a false alarm. In the past, we used criterion shift models to explain the high false alarm rate in the DRM false memory paradigm. More recently, we observed that some individuals willingly shift their decision criterion, while others will not shift their criteria at all. We are exploring the inherent characteristics that mediate an individual's willingness to shift their decision criterion when it is advantageous to do so. Further, we have exploited these individual differences in criterion shifting in order to better understand the fronto-parietal network of brain activity associated with successful memory recognition.

Hypothesis Formation and Evaluation

Miller Lab Research Summary

Areas in white denote regions associated with hypothesis formation and evaluation in healthy individuals.

One of the hallmarks of split-brain research is the left hemisphere's drive to interpret the world around it. Our goal is to understand and characterize this need of the human brain to form hypotheses. Specifically, we want to determine what propels an individual to seek an explanation, how hypotheses are generated, and what constitutes a good explanation. We are also interested in how the brain evaluates the plausibility and validity of its hypotheses. We believe the brains of healthy individuals strike a balance between hypothesis formation and evaluation, and a perturbation in this system may give rise to delusional disorders. Our ultimate goal is to uncover the neural processes that support hypothesis formation and evaluation in both healthy and deluded individuals.

Individual Variability in Brain Activity

Miller Lab Research Summary

Brain activity associated with memory retrieval for nine individuals. Notice the variability between individual brain maps.

Neuroimaging studies typically rely on maps of brain activity that are an average across a group of subjects in order to increase statistical power. However, our studies have demonstrated that an individual map of brain activity is not unlike a fingerprint in its uniqueness and relative stability over time. A reliance on group maps can leave out a wealth of information at the individual level. We seek to understand the sources of this variability in brain activity given the variable and dynamic nature of episodic memory and decision-making.

Partietal Lobe Contributions to Memory

Miller Lab Research Summary

Parietal lobe activations are a ubiquitous finding in neuroimaging studies of recognition memory, but the functionality of this region remains a mystery. We have explored this functionality using a variety of source monitoring tasks and by manipulating decision processes during recognition memory tasks.

Social Reasoning & Theory of Mind

Miller Lab Social Reasoning Research

In the real world, decision-making and reasoning usually occurs within a social context. We have conducted neuroimaging and patient studies that examine this issue with a consideration of specialized modules responsible for theory of mind attributions (that is, attributing beliefs and thoughts to other people).

Split Brain Research

Miller Lab Split Brain Research

In the past, our lab conducted studies of patients who had their corpus callosum surgically severed (now an obsolete treatment) due to severe epilepsy. These patients presented a rare opportunity to understand the unique functionality of each hemisphere in isolation and the effect of severing inter-hemispheric communication. These studies ranged in topics from episodic memory to probability matching to moral reasoning.

However, with the passing of patient JW in 2017, there are no more split-brain patients who are willing to participate in research marking the end of an era for cognitive neuroscience. For over a half-century split-brain research provided some of the most influential discoveries in human cognition.