Biomedical subjects

Marcia K Johnson

Publications and source records attributed to Marcia K Johnson.

5 recordsLinked to original sources

PubMed2003

Prefrontal activity associated with working memory and episodic long-term memory.

Many recent neuroimaging studies have highlighted the role of prefrontal regions in the sustained maintenance and manipulation of information over short delays, or working memory (WM). In addition, neuroimaging findings have highlighted the role of prefrontal regions in the formation and retrieval of memories for events, or episodic long-term memory (LTM), but it remains unclear whether these regions are distinct from those that support WM. We used event-related functional magnetic resonance imaging (fMRI) to identify patterns of prefrontal activity associated with encoding and recognition during WM and LTM tasks performed by the same subjects. Results showed that the same bilateral ventrolateral prefrontal regions (at or near Brodmann's Areas [BA] 6, 44, 45, and 47) and dorsolateral prefrontal regions (BA 9/46) were engaged during encoding and recognition within the context of WM and LTM tasks. In addition, a region situated in the left anterior middle frontal gyrus (BA 10/46) was engaged during the recognition phases of the WM and LTM tasks. These results support the view that the same prefrontal regions implement reflective processes that support both WM and LTM.

Adult↗

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

The development of explicit memory for basic perceptual features.

In three experiments with 164 individuals between 4 and 80 years old, we examined age-related changes in explicit memory for three perceptual features--item identity, color, and location. In Experiments 1-2, feature recognition was assessed in an incidental learning, gamelike task resembling the game Concentration. In Experiment 3, feature recognition was assessed using a pencil-and-paper task after intentional learning instructions. The form of the explicit memory function across the life span varied with the particular perceptual feature tested and the type of task. Item recognition was excellent at all ages but was significantly poorer for older adults than children, color recognition peaked in late childhood on the gamelike task, and location recognition peaked in early adulthood on the pencil-and-paper task. These findings indicate that performance on explicit memory tests is not a consistent inverted U-shaped function of age across various features. Explicit memory performance depends on what is measured and how. Because explicit memory typically reflects a composite of different features, age-related changes in explicit memory will not necessarily correspond to the function for any single one.

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↗