Biomedical subjects

Karen J Mitchell

Publications and source records attributed to Karen J Mitchell.

12 recordsLinked to original sources

PubMed2006

A functional magnetic resonance imaging investigation of short-term source and item memory for negative pictures.

We investigated the hypothesis that arousal recruits attention to item information, thereby disrupting working memory processes that help bind items to context. Using functional magnetic resonance imaging, we compared brain activity when participants remembered negative or neutral picture-location conjunctions (source memory) versus pictures only. Behaviorally, negative trials showed disruption of short-term source, but not picture, memory; long-term picture recognition memory was better for negative than for neutral pictures. Activity in areas involved in working memory and feature integration (precentral gyrus and its intersect with superior temporal gyrus) was attenuated on negative compared with neutral source trials relative to picture-only trials. Visual processing areas (middle occipital and lingual gyri) showed greater activity for negative than for neutral trials, especially on picture-only trials.

Adolescent↗

PubMed2006

Emotional arousal can impair feature binding in working memory.

To investigate whether emotional arousal affects memorial feature binding, we had participants complete a short-term source-monitoring task-remembering the locations of four different pictures over a brief delay. On each trial, the four pictures were all either high arousal, medium arousal, or low arousal. Memory for picture-location conjunctions decreased as arousal increased. In addition, source memory for the location of negative pictures was worse among participants with higher depression scores. Two subsequent functional magnetic resonance imaging experiments showed that relative to low-arousal trials, high- and medium-arousal trials resulted in greater activity in areas associated with visual processing (fusiform gyrus, middle temporal gyrus/middle occipital gyrus, lingual gyrus) and less activity in superior precentral gyrus and the precentral-superior temporal intersect. These findings suggest that arousal (and perhaps negative valence for depressed people) recruits attention to items thereby disrupting working memory processes that help bind features together.

Adolescent↗

PubMed2006

Mental rubbernecking to negative information depends on task context.

We previously demonstrated mental rubbernecking during the simple cognitive act of refreshing a just activated representation. Participants saw two neutral and one negative word presented simultaneously and, 425 msec later, were cued to mentally refresh (i.e., think of) one of the no-longer-present words. They were slower to refresh a neutral word than the negative word (Johnson et al., 2005, Experiment 6A). The present experiments extended that work by showing mental rubbernecking when negative items were sometimes the target of refreshing, but not when negative items were present but never the target of refreshing, indicating that expectations influence mental rubbernecking. How expectations might modulate the impact of emotional distraction is discussed.

Adolescent↗

PubMed2005

An fMRI investigation of short-term source memory in young and older adults.

Using functional magnetic resonance imaging (fMRI) and a working memory procedure, we compared source memory judgments (format and location) with old-new judgments in young and older adults. Consistent with previous fMRI findings, for young adults, an area of left dorsolateral prefrontal cortex showed greater activity during format than old-new judgments made immediately, as well as those made after a brief, filled delay. In contrast, for older adults, activity in this area was not greater during format than old-new judgments at either retention interval. These data provide additional evidence that left lateral prefrontal cortex is important in monitoring specific source information and new evidence that older adults' source memory deficits may be related, in part, to reduced function of this brain area.

Adult↗

PubMed2005

Using fMRI to investigate a component process of reflection: prefrontal correlates of refreshing a just-activated representation.

Using fMRI, we investigated the functional organization of prefrontal cortex (PFC) as participants briefly thought of a single just-experienced item (i.e., refreshed an active representation). The results of six studies, and a meta-analysis including previous studies, identified regions in left dorsolateral, anterior, and ventrolateral PFC associated in varying degrees with refreshing different types of information (visual and auditory words, drawings, patterns, people, places, or locations). In addition, activity increased in anterior cingulate with selection demands and in orbitofrontal cortex when a nonselected item was emotionally salient, consistent with a role for these areas in cognitive control (e.g., overcoming "mental rubbernecking"). We also found evidence that presenting emotional information disrupted an anterior component of the refresh circuit. We suggest that refreshing accounts for some neural activity observed in more complex tasks, such as working memory, long-term memory, and problem solving, and that its disruption (e.g., from aging or emotion) could have a broad impact.

Acoustic Stimulation↗

PubMed2004

Impaired performance in a working memory binding task in patients with schizophrenia.

This study investigated feature binding in a working memory task in patients with schizophrenia and in normal controls. Twenty-five patients and 25 controls participated. On each trial, three drawings of familiar objects were presented sequentially, each in a different cell of a 3 x 3 grid. In different blocks of trials, participants remembered either individual features (object and location conditions) or an object and its location (combination condition). The results showed that patients were slower and less accurate than controls under all conditions. Accuracy of both groups was reduced in the combination condition relative to the single-feature conditions, but patients showed disproportionately poorer performance in the combination condition than in the object and location conditions. Thus, patients with schizophrenia exhibit deficits in working memory, particularly when the task requires binding objects to their locations. This finding demonstrates that processes that establish coherent and temporary episodic representations in working memory are impaired in schizophrenia.

Adult↗

PubMed2004

Preserved spatial memory over brief intervals in older adults.

Two studies compared young and older adults' memory for location information after brief intervals. Experiment 1 found that accuracy of intentional spatial memory for individual locations was similar in young and older participants for set sizes of 3 and 6. Both groups also encoded individual locations in relation to the larger configuration of locations. Experiment 2 showed that like young adults, older adults' latency to respond to a test probe in a letter working memory task was negatively influenced by spatial information that was irrelevant to the task. This interference effect indicated preserved incidental memory for spatial information in older adults. Together, these data suggest that initial encoding of spatial information for relatively small numbers of items is largely preserved in healthy older adults and that representations of spatial information persist over short intervals.

Adolescent↗

PubMed2004

An age-related deficit in prefrontal cortical function associated with refreshing information.

Older adults are slower than young adults to think of an item they just saw, that is, to engage or execute (or both) the simple reflective operation of refreshing just-activated information. In addition, they derive less long-term memory benefit from refreshing information. Using functional magnetic resonance imaging (fMRI), we found that relative to young adults, older adults showed reduced refresh-related activity in an area of dorsolateral prefrontal cortex (left middle frontal gyrus, Brodmann's Area 9), but not in other refresh-related areas. This provides strong evidence that a frontal component of the circuit that subserves this basic cognitive process is especially vulnerable to aging. Such a refresh deficit could contribute to poorer performance of older than young adults on a wide range of cognitive tasks.

Adolescent↗

PubMed2003

FMRI evidence for an organization of prefrontal cortex by both type of process and type of information.

Neuroimaging evidence is conflicting regarding whether human prefrontal cortex (PFC) shows functional organization by type of processes engaged or type of information processed. Most studies use complex working or long-term memory tasks requiring multiple processes and the combinations of processes recruited for different materials may vary. Using functional magnetic resonance imaging (fMRI) and simple tasks suggested by a component process approach, we found activity in left PFC when participants thought about (refreshed) a just-seen item and in right PFC when participants noted whether an item had been presented previously. Furthermore, the distribution of activation in left or right PFC varied with type of information. Thus, at the component process level, PFC shows functional organization by both process and type of information.

Adult↗

PubMed2002

Neuroimaging a single thought: dorsolateral PFC activity associated with refreshing just-activated information.

Neuroimaging studies of human working memory (WM) show conflicting results regarding whether dorsolateral prefrontal cortex (PFC) contributes to maintaining information in consciousness or is recruited primarily when information must be manipulated. Using functional magnetic resonance imaging (fMRI), we looked at a minimal maintenance process--thinking back to a single, just-seen stimulus (refreshing). We found greater activity in left dorsolateral PFC (BA9) when participants refreshed a word compared to reading a word once or a second time. Furthermore, recognition memory was subsequently more accurate and faster for items that had been refreshed, demonstrating that a single thought that maintains activation can have consequences for long-term memory. Our fMRI results call into question any class of models of the functional organization of PFC and WM that associates simple and/or maintenance processes only with ventrolateral PFC or that associates dorsolateral PFC only with more complex processes such as manipulation.

Adult↗

PubMed2002

Second thoughts versus second looks: an age-related deficit in reflectively refreshing just-activated information.

Age-related deficits in memory are greater as encoding and retrieval tasks require more reflective (self-generated or executive) processing. One problem in developing more specific models of age-related changes in cognition is that the tasks studied tend to be complex and vary in the combinations of component cognitive processes they recruit. Here we report an age-related deficit in one of the most elementary, but critical, components of reflection: refreshing a just-activated representation. Impairment in such a process potentially has a wide-ranging impact on all higher-order cognition.

Adolescent↗

PubMedDate not supplied

Prefrontal cortex activity associated with source monitoring in a working memory task.

Using functional magnetic resonance imaging (fMRI), we investigated prefrontal cortex (PFC) activity during remembering specific source information (format, location judgments) versus remembering that could be based on undifferentiated information, such as familiarity (old/new recognition [ON], recency judgments). A working memory (WM) paradigm with an immediate test yielded greater activation in the lateral PFC for format and location source memory (SM) tasks than ON recognition; this SM-related activity was left lateralized. The same regions of PFC were recruited in Experiment 2 when information was tested immediately and after a filled delay. Substituting recency for location judgments (Experiment 3) resulted in an overall shift in task context that produced greater right PFC activity associated with ON and recency tasks compared to the format task, in addition to left SM-related activity. These data extend to WM previous findings from long-term memory (LTM) indicating that the left and right PFC may be differentially involved in memory attributions depending on the specificity of information evaluated. The findings also provide evidence for the continuity of evaluative processes recruited in WM and LTM.

Adult↗