Biomedical subjects

Tara A Cairo

Publications and source records attributed to Tara A Cairo.

5 recordsLinked to original sources

PubMed2006

Temporo-prefrontal coordination increases when semantic associations are strongly encoded.

Relational association of disparate semantic concepts can strengthen encoding of episodes. Previous research has shown that the left medial temporal lobe (MTL) and the left prefrontal cortex (PFC) are the primary brain regions activated during both verbal encoding and the association of disparate semantic concepts. In the current functional magnetic resonance imaging (fMRI) study, our goal was to compare the coordinated response of the left MTL and left PFC when disparate semantic associations are strongly encoded compared to when they are weakly encoded. To achieve this goal, subjects were scanned while creating sentences based on a presented pair of words, and were asked to free-recall these sentences at a later time. Half the word pairs were semantically unrelated, and half were semantically related. Analysis of relatedness activations (unrelated-related contrast) suggested that the PFC was active whether or not the items were free-recalled, and increased activation of the MTL was required to promote encoding. Analyses of coordination of relatedness activations comparing free-recalled items to not free-recalled items showed an increase in left MTL-left PFC coordination for relatedness activations on free-recalled items. These results suggest that formation of relational semantic associations that lead to strongly encoded episodes requires increased coordination of the left MTL-left PFC neural pathway.

Adolescent↗

PubMed2005

Decreased encoding efficiency in schizophrenia.

BACKGROUND: Working memory deficits are a cardinal feature of schizophrenia that contribute to social and occupational dysfunction. METHODS: We used functional magnetic resonance imaging to compare the response to varying task demands during the performance of an item recognition task. Study design and analysis procedures were optimized for the detection of load dependent activity during the encoding phase of working memory. RESULTS: At the lowest load conditions the schizophrenia group performed as well as controls, however to achieve this equivalent performance the schizophrenia group had a significantly higher magnitude of activation compared to the controls. At the higher load conditions, the magnitude of activation between groups became more similar and we began to see performance deficits in the schizophrenic group. CONCLUSIONS: These results suggest that patients with schizophrenia have decreased efficiency in the cognitive processes that underlie the early encoding phase of this task. For lower demand tasks, patients with schizophrenia can compensate for decreased efficiency by working harder to achieve equivalent performance. Encoding utilizes attentional and perceptual cognitive operations that are likely common to many other cognitive tasks; therefore, inefficiency may underlie the deficits observed in a wide range of cognitive tasks in schizophrenia compared to healthy controls.

Adult↗

PubMed2005

Processing efficiency of a verbal working memory system is modulated by amphetamine: an fMRI investigation.

RATIONALE: Working memory performance may be improved or decreased by amphetamine, depending on baseline working memory capacity and amphetamine dosage. This variable effect suggests an optimal range of monaminergic activity for working memory, either below or above which it is compromised. We directly tested this possibility with human participants by varying amphetamine dosage and measuring the efficiency of cortical processing in brain regions associated with working memory. OBJECTIVES: The modulation of cortical processing in a verbal working memory network by dextroamphetamine (D-amph) was examined using BOLD functional magnetic resonance imaging (fMRI) with healthy participants. The goal of the study was to test the hypothesis of an inverted U-shaped relationship between D-amph dose and processing efficiency of a verbal working memory system. METHODS: D-amph dosage was increased cumulatively every 2 h across four scanning sessions collected in a single day. The primary measure used for analyses in this study was the extent of activation in brain regions empirically defined as a working memory network. RESULTS: An inverted U-shaped relationship was observed between the amount of D-amph administered and working memory processing efficiency. This relationship was specific to brain areas functionally defined as working memory regions and to the encoding/maintenance phase (as opposed to the response phase) of the task. CONCLUSION: The results are consistent with the hypothesis that the neurochemical effects of amphetamine modulate the efficiency of a verbal working memory system. The effect of amphetamine on working memory in healthy individuals may provide insight regarding the working memory deficits seen in schizophrenia, given the overlap between neurochemical systems affected by amphetamine, and those disordered in schizophrenia.

Adult↗

PubMed2004

The influence of working memory load on phase specific patterns of cortical activity.

This study investigated patterns of cortical activity associated with the temporally separated encoding, maintenance and retrieval phases of a working memory (WM) task. Eighteen healthy subjects completed a variable load version of the Sternberg Item Recognition Task. Brain regions showing activity on average across load were determined for each task phase. In addition, brain regions showing activity that increased linearly with load were determined for encoding and retrieval. Although previous fMRI studies have used event-related designs to isolate phase specific activity, this study differed in that design and analysis methods were optimized to ensure low multicollinearity between the conditions of interest: the duration of the intermediate phase (maintenance) was varied and load was selectively modeled for the encoding and retrieval phases. The brain areas showing activity on average across load for each phase combine to encompass regions identified in previous studies that have not attempted to separate phase specific activity. Encoding is associated with extensive load dependent activity, with the most robust activity in bilateral occipital and posterior parietal regions. Retrieval is associated with more selective load dependent activity, primarily in the anterior supplementary motor region and the right posterior cerebellum. The analysis strategies employed in this study could be used to further delineate the phases of WM that are most severely compromised in clinical populations with WM disturbances.

Adolescent↗

PubMed2003

Abnormal processing of speech during oddball target detection in schizophrenia.

Healthy subjects show increased activation in left temporal lobe regions in response to speech sounds compared to complex nonspeech sounds. Abnormal lateralization of speech-processing regions in the temporal lobes has been posited to be a cardinal feature of schizophrenia. Event-related fMRI was used to test the hypothesis that schizophrenic patients would show an abnormal pattern of hemispheric lateralization when detecting speech compared with complex nonspeech sounds in an auditory oddball target-detection task. We predicted that differential activation for speech in the vicinity of the superior temporal sulcus would be greater in schizophrenic patients than in healthy subjects in the right hemisphere, but less in patients than in healthy subjects in the left hemisphere. Fourteen patients with schizophrenia (selected from an outpatient population, 2 females, 12 males, mean age 35.1 years) and 29 healthy subjects (8 females, 21 males, mean age 29.3 years) were scanned while they performed an auditory oddball task in which the oddball stimuli were either speech sounds or complex nonspeech sounds. Compared to controls, individuals with schizophrenia showed greater differential activation between speech and nonspeech in right temporal cortex, left superior frontal cortex, and the left temporal-parietal junction. The magnitude of the difference in the left temporal parietal junction was significantly correlated with severity of disorganized thinking. This study supports the hypothesis that aberrant functional lateralization of speech processing is an underlying feature of schizophrenia and suggests the magnitude of the disturbance in speech-processing circuits may be associated with severity of disorganized thinking.

Adult↗