Theroles of the hippocampus and prefrontal cortex during visual long-term memory:

Thesis advisor: Scott D. SlotnickWe are able to consciously remember an incredible amount of information for long periods of time (Brady et al., 2008, 2013). Furthermore, we often think about our memories in terms of how successful we are in retrieving them, such as vividly recalling the smell of your grandmother’s cooking. However, we can also identify the times when we have forgotten information, such as misremembering the name of an acquaintance or misplacing your car keys. Such instances of forgetting have been suggested to be caused by inhibitory processes acting on associated information, such as the inhibitory processing shown in retrieval-induced forgetting where the retrieval of specific items leads to forgetting related information (Anderson et al., 2004; Wimber et al., 2015). Thus, long-term memory is said to rely on both accurately retrieving specific details and inhibiting potentially distracting information. In Chapter 1, I demonstrate that specificity of long-term memory depends on inhibiting related information through a series of behavioral experiments investigating item memory for faces and abstract shapes. In Chapter 2 and Chapter 3, I examine the neural regions associated with long-term memory specificity and inhibitory processing by focusing on the functional roles of the hippocampus and the prefrontal cortex, two key regions associated with long-term memory. In Chapter 2, I provide evidence that the hippocampus is associated with memory specificity by demonstrating that distinct regions of the hippocampus are associated with memory for different visual field locations. Furthermore, I provide evidence that the hippocampus operates in continuous manner during recollection (i.e., conscious retrieval of details). In Chapter 3, I demonstrate that the prefrontal cortex can inhibit both the hippocampus and language processing regions during retrieval of distracting information during episodic and semantic memory, respectively.Thesis (PhD) — Boston College, 2019.Submitted to: Boston College. Graduate School of Arts and Sciences.Discipline: Psychology

The Effect of Pre-Event Instructions on Eyewitness Identification

Research on eyewitness identification often involves exposing participants to a simulated crime and later testing memory using a lineup. We conducted a systematic review showing that pre-event instructions, instructions given before event exposure, are rarely reported and those that are reported vary in the extent to which they warn participants about the nature of the event or tasks. At odds with the experience of actual witnesses, some studies use pre-event instructions explicitly warning participants of the upcoming crime and lineup task. Both the basic and applied literature provide reason to believe that pre-event instructions may affect eyewitness identification performance. In the current experiment, we tested the impact of pre-event instructions on lineup identification decisions and confidence. Participants received non-specific pre-event instructions (i.e., “watch this video”) or eyewitness pre-event instructions (i.e., “watch this crime video, you’ll complete a lineup later”) and completed a culprit-absent or -present lineup. We found no support for the hypothesis that participants who receive eyewitness pre-event instructions have higher discriminability than participants who receive non-specific pre-event instructions. Additionally, confidence-accuracy calibration was not significantly different between conditions. However, participants in the eyewitness condition were more likely to see the event as a crime and to make an identification than participants in the non-specific condition. Implications for conducting and interpreting eyewitness identification research and the basic research on instructions and attention are discussed

The Anterior Prefrontal Cortex and the Hippocampus Are Negatively Correlated during False Memories

False memories commonly activate the anterior/dorsolateral prefrontal cortex (A/DLPFC) and the hippocampus. These regions are assumed to work in concert during false memories, which would predict a positive correlation between the magnitudes of activity in these regions across participants. However, the A/DLPFC may also inhibit the hippocampus, which would predict a negative correlation between the magnitudes of activity in these regions. In the present functional magnetic resonance imaging (fMRI) study, during encoding, participants viewed abstract shapes in the left or right visual field. During retrieval, participants classified each old shape as previously in the “left” or “right” visual field followed by an “unsure”–“sure”–“very sure” confidence rating. The contrast of left-hits and left-misses produced two activations in the hippocampus and three activations in the left A/DLPFC. For each participant, activity associated with false memories (right–“left”–“very sure” responses) from the two hippocampal regions was plotted as a function of activity in each A/DLPFC region. Across participants, for one region in the left anterior prefrontal cortex, there was a negative correlation between the magnitudes of activity in this region and the hippocampus. This suggests that the anterior prefrontal cortex might inhibit the hippocampus during false memories and that participants engage either the anterior prefrontal cortex or the hippocampus during false memories

Inhibition in face memory specificity

Stimuli and data (SPSS data file) for the paper "The role of individual differences in face recognition and mental imagery on face-memory specificity and inhibition

The Anterior Prefrontal Cortex and the Hippocampus Are Negatively Correlated during False Memories

False memories commonly activate the anterior/dorsolateral prefrontal cortex (A/DLPFC) and the hippocampus. These regions are assumed to work in concert during false memories, which would predict a positive correlation between the magnitudes of activity in these regions across participants. However, the A/DLPFC may also inhibit the hippocampus, which would predict a negative correlation between the magnitudes of activity in these regions. In the present functional magnetic resonance imaging (fMRI) study, during encoding, participants viewed abstract shapes in the left or right visual field. During retrieval, participants classified each old shape as previously in the “left” or “right” visual field followed by an “unsure”–“sure”–“very sure” confidence rating. The contrast of left-hits and left-misses produced two activations in the hippocampus and three activations in the left A/DLPFC. For each participant, activity associated with false memories (right–“left”–“very sure” responses) from the two hippocampal regions was plotted as a function of activity in each A/DLPFC region. Across participants, for one region in the left anterior prefrontal cortex, there was a negative correlation between the magnitudes of activity in this region and the hippocampus. This suggests that the anterior prefrontal cortex might inhibit the hippocampus during false memories and that participants engage either the anterior prefrontal cortex or the hippocampus during false memories

Spatial Memory Activity Distributions Indicate the Hippocampus Operates in a Continuous Manner

There is a long-standing debate as to whether recollection is a continuous/graded process or a threshold/all-or-none process. In the current spatial memory functional magnetic resonance imaging (fMRI) study, we examined the hippocampal activity distributions—the magnitude of activity as a function of memory strength—to determine the nature of processing in this region. During encoding, participants viewed abstract shapes in the left or right visual field. During retrieval, old shapes were presented at fixation and participants classified each shape as previously in the “left” or “right” visual field followed by an “unsure”–“sure”–“very sure” confidence rating. The contrast of left-hits and left-misses produced two activations in the hippocampus. The hippocampal activity distributions for left shapes and right shapes were completely overlapping. Critically, the magnitude of activity associated with right-miss-very sure responses was significantly greater than zero. These results support the continuous model of recollection, which predicts overlapping activity distributions, and contradict the threshold model of recollection, which predicts a threshold above which only one distribution exists. Receiver operating characteristic analysis did not distinguish between models. The present results demonstrate that the hippocampus operates in a continuous manner during recollection and highlight the utility of analyzing activity distributions to determine the nature of neural processing

The anterior hippocampus is associated with spatial memory encoding

There are many hypotheses regarding specialization of the anterior versus posterior hippocampus including memory encoding versus retrieval and other cognitive processes versus spatial memory. In the present functional magnetic resonance imaging study, we distinguished between the hypothesis linking encoding to the anterior hippocampus and the hypothesis linking spatial memory to the posterior hippocampus by evaluating whether spatial memory encoding involved the anterior hippocampus or the posterior hippocampus. During encoding, participants viewed abstract shapes in each of four visual field quadrants while instructed to maintain central fixation. During retrieval, old shapes were presented at fixation and participants identified the previous quadrant of each shape. A general linear model analysis did not reveal encoding activations in the anterior or posterior hippocampus. These results motivated a multi-voxel pattern analysis to assess whether there were distinct patterns of activity associated with encoding shapes in each quadrant within the anterior or posterior hippocampus. For each participant, patterns of activity associated with each quadrant were split by run (i.e., odd runs versus even runs) and the patterns in half the data were used to classify patterns in the other half of the data. Classification accuracy for items at encoding, collapsed over subsequent accuracy, was significantly above chance in the anterior but not posterior hippocampus. The present findings indicate that spatial memory encoding is associated with patterns of activity in the anterior hippocampus

The Effect of Pre-Event Instructions on Eyewitness Identification Stage 2 Registered Report Accepted Manuscript

Research on eyewitness identification often involves exposing participants to a simulated crime and later testing memory using a lineup. We conducted a systematic review showing that pre-event instructions, instructions given before event exposure, are rarely reported and those that are reported vary in the extent to which they warn participants about the nature of event or tasks. At odds with the experience of actual witnesses, some studies use pre-event instructions explicitly warning participants of the upcoming crime and lineup task. Both the basic and applied literature provide reason to believe that pre-event instructions may impact eyewitness identification performance. In Experiment 1, we will test the effect of pre-event instructions on lineup identification decisions and confidence. Participants will receive non-specific pre-event instructions (i.e., “watch this video”) or eyewitness pre-event instructions (i.e., “watch this crime video, you’ll complete a line-up later”) and complete a culprit absent or present lineup. In Experiment 2, we will manipulate exposure duration and pre-event instructions to determine if pre-event instructions differentially impact high or low quality eyewitness events. If pre-event instructions impact eyewitness identification accuracy, then the findings of existing studies need to be considered in the context of their pre-event instructions and future work will be needed to determine how instructions interact with existing systems and estimator variables