Biomedical subjects

Lee Ryan

Publications and source records attributed to Lee Ryan.

9 recordsLinked to original sources

PubMed2007

Caffeine attenuates practice effects in word stem completion as measured by fMRI BOLD signal.

Caffeine ingestion results in increased brain cell metabolism (Nehlig et al. [1992] Brain Res Brain Res Rev 17:139-170) and decreased cerebral blood flow (Field et al. [2003] Radiology 227:129-135; Mulderink et al. [2002] Neuroimage 15:37-44). The current study investigated the effect of caffeine in a word stem completion task using only novel word stems (no repeated stimuli). Resting perfusion was measured with arterial spin labeled perfusion MRI, along with blood oxygenation level-dependent (BOLD) signal before and after ingestion of regular coffee, decaffeinated coffee, and water. Based on previous research (Laurienti et al. [2002] Neuroimage 17:751-757; Mulderink et al. [2002] Neuroimage 15:37-44), we hypothesized that caffeine would result in increased BOLD signal intensity and extent of BOLD activation. As expected, caffeine resulted in a significant decrease in cerebral perfusion. However, both the control and caffeine groups showed an increase in BOLD signal amplitude across two sets of novel word stems. Additionally, the control group showed a 50% reduction in the extent of BOLD activation, while the caffeine group showed no change in activation extent. Neither group showed changes in BOLD baseline signal over time, which had been suggested to mediate caffeine-related BOLD signal changes. The results suggest that caffeine may attenuate general task practice effects that have been described in recent functional MRI studies of word stem completion (Buckner et al. [2000] Brain 123:620-640).

Adolescent↗

PubMed2006

Regional specificity of format-specific priming effects in mirror word reading using functional magnetic resonance imaging.

The speed and accuracy with which subjects can read words is enhanced or "primed" by a prior presentation of the same words. Moreover, priming effects are generally larger when the physical form of the words is maintained from the first to the second presentation. We investigated the neural basis of format-specific priming in a mirror word-reading task using event-related functional magnetic resonance imaging (fMRI). Participants read words that were presented either in mirror-image (M) orientation or in normal (N) orientation and were repeated either in the same or the alternate orientation, creating 4 study-test conditions, N-N, M-N, N-M, and M-M. Priming of N words resulted in reductions in fMRI signal in multiple brain regions, even though reading times (RTs) were unchanged. Priming of M words showed a pattern of RTs consistent with format-specific priming, with greater reductions when the prime matched the form of the test word. Priming-related reductions in fMRI activity were evident in all regions involved in mirror-image reading, regardless of the orientation of the prime. Importantly, reductions in several posterior regions, including fusiform, superior parietal, and superior temporal regions were also format specific. That is, signal reductions in these regions were greatest when the visual form of the prime and target matched (M-M compared with N-M). The results indicate that, although there are global neural priming effects due to stimulus repetition, it is also possible to identify regional brain changes that are sensitive to the specific perceptual overlap of primes and targets.

Adult↗

PubMed2006

The impact of stress on neutral and emotional aspects of episodic memory.

The present experiment demonstrates that exposure to a significant psychological stressor (administered before watching a slide show) preserves or even enhances memory for emotional aspects of an event, and simultaneously disrupts memory for non-emotional aspects of the same event. Stress exposure also disrupted memory for information that was visually and thematically central to the event depicted in the slide show. Memory for peripheral information, on the other hand, was unaffected by stress. These results are consistent with theories invoking differential effects of stress on brain systems responsible for encoding and retrieving emotional memories (the amygdala) and non-emotional memories (e.g., the hippocampal formation), and inconsistent with the view that memories formed under high levels of stress are qualitatively the same as those formed under ordinary emotional circumstances. These data, which are also consistent with results obtained in a number of studies using animals and humans, have implications for the traumatic memory debate and theories regarding human memory.

Amygdala↗

PubMed2004

A case of psychogenic fugue: I understand, aber ich verstehe nichts.

Psychogenic fugue is a disorder of memory that occurs following emotional or psychological trauma and results in a loss of one's personal past including personal identity. This paper reports a case of psychogenic fugue in which the individual lost access not only to his autobiographical memories but also to his native German language. A series of experiments compared his performance on a variety of memory and language tests to several groups of control participants including German-English bilinguals who performed the tasks normally or simulated amnesia for the German language. Neuropsychological, behavioral, electrophysiological and functional neuroimaging tests converged on the conclusion that this individual suffered an episode of psychogenic fugue, during which he lost explicit knowledge of his personal past and his native language. At the same time, he appeared to retain implicit knowledge of autobiographical facts and of the semantic or associative structure of the German language. The patient's poor performance on tests of executive control and reduced activation of frontal compared to parietal brain regions during lexical decision were suggestive of reduced frontal function, consistent with models of psychogenic fugue proposed by Kopelman and Markovitsch.

Adult↗

PubMed2004

Bilateral hippocampal volume predicts verbal memory function in temporal lobe epilepsy.

The present study used quantitative volume estimates of the hippocampus based on structural magnetic resonance imaging (MRI) to predict memory performance of individuals with epilepsy of temporal lobe origin (TLE). Twenty individuals with TLE completed standardized neuropsychological tests and a quality of life inventory, and participated in a brain MRI protocol designed to obtain high-resolution images of the hippocampus. The combined volume of the left and right hippocampi was found to be the best predictor of objective verbal memory performance. This finding is consistent with the functional adequacy model of hippocampal function. In contrast, the asymmetry between right and left hippocampal volume was the best predictor of subjective ratings of cognitive functioning, which is consistent with the functional reserve model. The collective and complementary functions of the left and right hippocampi merit further exploration in prospective studies of memory function and TLE.

Adult↗

PubMed2004

An fMRI study of episodic memory: retrieval of object, spatial, and temporal information.

Sixteen participants viewed a videotaped tour of 4 houses that highlighted a series of objects and their spatial locations. Participants were tested for memory of object, spatial, and temporal-order information while undergoing functional magnetic resonance imaging. Preferential activation was observed in the right parahippocampal gyrus during the retrieval of spatial-location information. Retrieval of contextual information (spatial location and temporal order) was associated with activation in the right dorsolateral prefrontal cortex. In bilateral posterior parietal regions, greater activation was associated with processing of visual scenes regardless of the memory judgment. These findings support current theories positing roles for frontal and medial temporal regions during episodic retrieval and suggest a specific role for the hippocampal complex in the retrieval of spatial-location information.

Adult↗

PubMed2004

The effects of a typing task on the hand volume of the older worker.

UNLABELLED: Few studies have examined the relationship between changes in hand volume and typing. Volumetric evaluation documents the presence of an inflammatory response to activity. METHOD: To study this relationship, researchers used a convenience sample of 31 participants who were aged 45 and older and worked full time where they typed at least one hour per day. Volumetric measurements were taken before a 15-minute typing activity, immediately after and 10 minutes after typing. Before typing, ergonomic adjustments were made to computer workstations, when necessary. Participants typed using an advanced speed test of the Mavis Beacon Teaches Typing program, which calculated adjusted words per minute. RESULTS: The data showed no significant (F = 0.321, p > 0.05) change in hand volume resulting from the typing activity. CONCLUSION: The amount of exercise provided in this study, a fifteen minute typing activity, did not result in changed hand volume.

Aged↗

PubMed2002

Masked word repetition results in increased fMRI signal: a framework for understanding signal changes in priming.

Evidence from multiple paradigms has converged on the finding that stimulus repetition most often results in decreases in neural activity. The mechanisms of these decreases, however, are not yet well understood. The current study attempted to determine, through the use of masked word repetition priming, whether decreases in activity levels occur in response to pre- or post-prime identification processes. fMRI was performed while participants engaged in a lexical decision task where words were primed with a briefly presented and masked word. Masked word priming resulted in increased fMRI signal in regions of cortex associated with the perceptual identification of the target words. This finding provides evidence suggesting that the impact of repetition priming on the fMRI signal may depend upon whether or not the prime is identified.

Adolescent↗

PubMed2002

Caffeine reduces time-of-day effects on memory performance in older adults.

For most older adults, memory performance depends on the time of day, with performance being optimal early in the morning and declining during the late afternoon hours. In the present study, we asked whether this decline could be ameliorated by a simple stimulant, caffeine. Adults over the age of 65 who considered themselves "morning types" were tested twice over an interval of 5 to 11 days, once in the morning and once in the late afternoon. Participants ingested either coffee with caffeine or decaffeinated coffee at both sessions. Participants who ingested decaffeinated coffee showed a significant decline in memory performance from morning to afternoon. In contrast, those who ingested caffeine showed no decline in performance from morning to afternoon. The results suggest that time-of-day effects may be mediated by nonspecific changes in level of arousal.

Age Factors↗