Elaboration versus suppression of cued memories: influence of memory recall instruction and success on parietal lobe, default network, and hippocampal activity.

Functional imaging studies of episodic memory retrieval consistently report task-evoked and memory-related activity in the medial temporal lobe, default network and parietal lobe subregions. Associated components of memory retrieval, such as attention-shifts, search, retrieval success, and post-retrieval processing also influence regional activity, but these influences remain ill-defined. To better understand how top-down control affects the neural bases of memory retrieval, we examined how regional activity responses were modulated by task goals during recall success or failure. Specifically, activity was examined during memory suppression, recall, and elaborative recall of paired-associates. Parietal lobe was subdivided into dorsal (BA 7), posterior ventral (BA 39), and anterior ventral (BA 40) regions, which were investigated separately to examine hypothesized distinctions in sub-regional functional responses related to differential attention-to-memory and memory strength. Top-down suppression of recall abolished memory strength effects in BA 39, which showed a task-negative response, and BA 40, which showed a task-positive response. The task-negative response in default network showed greater negatively-deflected signal for forgotten pairs when task goals required recall. Hippocampal activity was task-positive and was influenced by memory strength only when task goals required recall. As in previous studies, we show a memory strength effect in parietal lobe and hippocampus, but we show that this effect is top-down controlled and sensitive to whether the subject is trying to suppress or retrieve a memory. These regions are all implicated in memory recall, but their individual activity patterns show distinct memory-strength-related responses when task goals are varied. In parietal lobe, default network, and hippocampus, top-down control can override the commonly identified effects of memory strength

Search-Related Suppression of Hippocampus and Default Network Activity during Associative Memory Retrieval

Episodic memory retrieval involves the coordinated interaction of several cognitive processing stages such as mental search, access to a memory store, associative re-encoding, and post-retrieval monitoring. The neural response during memory retrieval is an integration of signals from multiple regions that may subserve supportive cognitive control, attention, sensory association, encoding, or working memory functions. It is particularly challenging to dissociate contributions of these distinct components to brain responses in regions such as the hippocampus, which lies at the interface between overlapping memory encoding and retrieval, and “default” networks. In the present study, event-related functional magnetic resonance imaging (fMRI) and measures of memory performance were used to differentiate brain responses to memory search from subcomponents of episodic memory retrieval associated with successful recall. During the attempted retrieval of both poorly and strongly remembered word pair associates, the hemodynamic response was negatively deflected below baseline in anterior hippocampus and regions of the default network. Activations in anterior hippocampus were functionally distinct from those in posterior hippocampus and negatively correlated with response times. Thus, relative to the pre-stimulus period, the hippocampus shows reduced activity during intensive engagement in episodic memory search. Such deactivation was most salient during trials that engaged only pre-retrieval search processes in the absence of successful recollection or post-retrieval processing. Implications for interpretation of hippocampal fMRI responses during retrieval are discussed. A model is presented to interpret such activations as representing modulation of encoding-related activity, rather than retrieval-related activity. Engagement in intensive mental search may reduce neural and attentional resources that are otherwise tonically devoted to encoding an individual’s stream of experience into episodic memory

Elaboration versus suppression of cued memories: influence of memory recall instruction and success on parietal lobe, default network, and hippocampal activity.

Functional imaging studies of episodic memory retrieval consistently report task-evoked and memory-related activity in the medial temporal lobe, default network and parietal lobe subregions. Associated components of memory retrieval, such as attention-shifts, search, retrieval success, and post-retrieval processing also influence regional activity, but these influences remain ill-defined. To better understand how top-down control affects the neural bases of memory retrieval, we examined how regional activity responses were modulated by task goals during recall success or failure. Specifically, activity was examined during memory suppression, recall, and elaborative recall of paired-associates. Parietal lobe was subdivided into dorsal (BA 7), posterior ventral (BA 39), and anterior ventral (BA 40) regions, which were investigated separately to examine hypothesized distinctions in sub-regional functional responses related to differential attention-to-memory and memory strength. Top-down suppression of recall abolished memory strength effects in BA 39, which showed a task-negative response, and BA 40, which showed a task-positive response. The task-negative response in default network showed greater negatively-deflected signal for forgotten pairs when task goals required recall. Hippocampal activity was task-positive and was influenced by memory strength only when task goals required recall. As in previous studies, we show a memory strength effect in parietal lobe and hippocampus, but we show that this effect is top-down controlled and sensitive to whether the subject is trying to suppress or retrieve a memory. These regions are all implicated in memory recall, but their individual activity patterns show distinct memory-strength-related responses when task goals are varied. In parietal lobe, default network, and hippocampus, top-down control can override the commonly identified effects of memory strength

I know I’ve seen you before: Distinguishing recent-single-exposure-based familiarity from pre-existing familiarity

This study examines how individuals differentiate recent-single-exposure-based familiarity from pre-existing familiarity. If these are two distinct cognitive processes, are they supported by the same neural bases? This study examines how recent-single-exposure-based familiarity and multiple-previous-exposure-based familiarity are supported and represented in the brain using functional MRI. In a novel approach, we first behaviorally show that subjects can divide retrieval of items in pre-existing memory into judgments of recollection and familiarity. Then, using functional magnetic resonance imaging, we examine the differences in blood oxygen level dependent activity and regional connectivity during judgments of recent-single-exposure-based and pre-existing familiarity. Judgments of these two types of familiarity showed distinct regions of activation in a whole-brain analysis, in medial temporal lobe (MTL) substructures, and in MTL substructure functional-correlations with other brain regions. Specifically, within the MTL, perirhinal cortex showed increased activation during recent-single-exposure-based familiarity while parahippocampal cortex showed increased activation during judgments of pre-existing familiarity. We find that recent-single-exposure-based and pre-existing familiarity are represented as distinct neural processes in the brain; this is supported by differing patterns of brain activation and regional correlations. This spatially distinct regional brain involvement suggests that the two separate experiences of familiarity, recent-exposure-based familiarity and pre-existing familiarity, may be cognitively distinct

Clinical validation of an optimized multimodal neurocognitive assessment of chronic mild TBI

ObjectivePrevious laboratory-based studies have shown that neurocognitive eye-tracking metrics are sensitive to chronic effects of mild traumatic brain injury (mTBI), even in individuals with normal performance on traditional neuropsychological measures. In this study, we sought to replicate and extend these findings in a military medical environment. We expected that metrics from the multimodal Fusion n-Back test would successfully distinguish chronic mTBI participants from controls, particularly eye movement metrics from the more cognitively challenging "1-Back" subtest.MethodsWe compared performance of participants with chronic mTBI (n = 46) and controls (n = 33) on the Fusion n-Back test and a battery of conventional neuropsychological tests. Additionally, we examined test reliability and the impact of potential confounds to neurocognitive assessment.ResultsOur results supported hypotheses; Fusion 1-Back metrics were successful in multimodal (saccadic and manual) classification of chronic mTBI versus control. In contrast, conventional neuropsychological measures could not distinguish these groups. Additional findings demonstrated the reliability of Fusion n-Back test metrics and provided evidence that saccadic metrics are resistant to confounding influences of age, intelligence, and psychiatric symptoms.InterpretationThe Fusion n-Back test could provide advantages in differential diagnosis for complex brain injury populations. Additionally, the rapid administration of this test could be valuable for screening patients in clinical settings where longer test batteries are not feasible

Task instruction and recall success influence the default network.

<p><i>Below</i>, Activity identified in the default network (yellow), revealed by the task minus fixation contrast. Significant clusters (<i>p</i><.01) used to extract average activity for each task condition, for both remembered and forgotten responses. Within the recall and elaborative recall conditions, there was greater suppression of activity for forgotten pairs compared to remembered pairs; *** <i>p</i><.001. Activity presented on an average anatomical brain of all 12 study participants. Error bars represent standard error of the mean.</p

Study design.

<p>Each subject participated in the pre-scan study session outside of the scanner. Subjects were asked to memorize 60 pairs of images that were learned to 100% criterion. During scanning, subjects performed the event-related task in which they were asked to either ‘suppress,’ ‘recall,’ or ‘elaboratively recall’ the pair of the item presented. Trials were interleaved with a jittered fixation cross baseline.</p

Activation during suppression, recall, and elaborative recall differs for subregions of the parietal lobe.

<p>Activation in Brodmann Areas 7 (magenta), 40 (yellow), and 39 (cyan). Impulse response curves for suppress (A, E, I), recall (B, F, J), and elaborative recall (C, G, K) remembered and forgotten trials and difference scores (D, H, L) representing the difference in activation for remembered trials versus forgotten trials plotted for suppress (red), recall (blue), and elaborative recall (green) trials. Impulse response curves and difference plots for the A–D) dorsal parietal (BA 7) E–H) anterior ventral parietal (BA 40), and I–L) posterior ventral parietal (BA 39) cortices. Brodmann Areas presented on a standard brain. Error bars represent standard error of the mean, * <i>p</i><.05, ** <i>p</i><.01.</p