Biomedical subjects

Kristen A Lindgren

Publications and source records attributed to Kristen A Lindgren.

7 recordsLinked to original sources

PubMed2006

Function and connectivity in human primary auditory cortex: a combined fMRI and DTI study at 3 Tesla.

Human primary auditory cortex (PAC) is functionally organized in a tonotopic manner. Past studies have used neuroimaging to characterize tonotopic organization in PAC and found similar organization as that described in mammals. In contrast to what is known about PAC in primates and nonprimates, in humans, the structural connectivity within PAC has not been defined. In this study, stroboscopic event-related functional magnetic resonance imaging (fMRI) was utilized to reveal mirror symmetric tonotopic organization consisting of a high-low-high frequency gradient in PAC. Furthermore, diffusion tensor tractography and probabilistic mapping was used to study projection patterns within tonotopic areas. Based on earlier physiological and histological work in nonhuman PAC, we hypothesized the existence of cross-field isofrequency (homotopic) and within-field non-isofrequency (heterotopic)-specific axonal projections in human PAC. The presence of both projections types was found in all subjects. Specifically, the number of diffusion tensor imaging (DTI) reconstructed fibers projecting between high- and low-frequency regions was greater than those fibers projecting between 2 high-frequency areas, the latter of which are located in distinct auditory fields. The fMRI and DTI results indicate that functional and structural properties within early stages of the auditory processing stream are preserved across multiple mammalian species at distinct evolutionary levels.

Acoustic Stimulation↗

PubMed2005

Intact hemispheric specialization for spatial and shape working memory in schizophrenia.

OBJECTIVE: Using functional MRI, we investigated whether, like healthy subjects, patients with schizophrenia show a relative hemispheric specialization in ventrolateral prefrontal cortex (PFC) for spatial and shape working memory (WM). We hypothesized that reduced specialization in schizophrenia would reflect a failure to adopt optimal domain-specific strategies and would contribute to WM deficits. METHODS: Twelve healthy subjects and 16 schizophrenia patients performed spatial and shape WM tasks and a non-WM control task. Direct comparisons of the spatial and shape WM tasks assessed specialization. RESULTS: Despite deficient WM performance, both patients and controls showed a relative hemispheric specialization in ventrolateral PFC for spatial (right) and shape (left) WM and did not differ in this regard. CONCLUSIONS: The finding of intact hemispheric specialization in ventrolateral PFC suggests that patients employ the same domain-specific strategies as healthy subjects during spatial and shape WM. Rather than reflecting a failure to adopt the optimal strategy, we hypothesize that WM deficits in schizophrenia reflect impairments of executive processes that are required for WM performance regardless of domain. These processes are associated with activity in the dorsolateral PFC, a region that has been repeatedly implicated in studies of WM.

Adult↗

PubMed2005

What is perseverated in schizophrenia? Evidence of abnormal response plasticity in the saccadic system.

Although perseveration is sometimes attributed to defective set switching, the authors have recently shown that set-switching is normal in schizophrenia. In this article, the authors tested for persistent states of the saccadic response system, rather than set perseveration. Schizophrenic and healthy subjects performed antisaccades and prosaccades. The authors analyzed for 3 carry-over effects. First, whereas the latency of the current saccade correlated with that of the prior saccade in both groups, the correlations under mixed-task conditions declined in healthy but not in schizophrenic subjects. Second, antisaccades in penultimate trials delayed upcoming saccades in schizophrenic but not in healthy subjects. Third, schizophrenic subjects were more likely to erroneously perseverate the direction of a prior antisaccade but not a prior prosaccade. The authors concluded that, in schizophrenia, the effects of correct antisaccades are persistent not weak. Saccades in schizophrenia are characterized by perseveration of antisaccade-induced changes in the saccadic response system rather than failures to switch task set.

Adult↗

PubMed2004

The relationship of saccadic peak velocity to latency: evidence for a new prosaccadic abnormality in schizophrenia.

Antisaccades have not only longer latencies but also lower peak velocities than prosaccades. It is not known whether these latency and velocity differences are related. Studies of non-human primates suggest that prosaccade peak velocity declines as latency from target appearance increases. We examined whether a similar relationship between peak velocity and latency existed in human saccades, whether it accounted for the difference in peak velocity between antisaccades and prosaccades, and whether it was affected by schizophrenia, a condition that affects antisaccade performance. Sixteen control and 21 schizophrenia subjects performed prosaccade and antisaccade trials in the same test session. In both groups antisaccades had lower peak velocities than prosaccades. Latency did not influence the peak velocities of antisaccades in either subject group. At short latencies, the peak velocities of prosaccades were also similar in the two groups. However, while prosaccade peak velocities declined minimally with increasing latency in control subjects, those in the schizophrenia group declined significantly until they reached a value similar to antisaccade peak velocities. We conclude that, in normal subjects, the effect of latency on prosaccade peak velocity is minimal and cannot account for the lower velocity of antisaccades. In schizophrenia, we hypothesize that the latency-related decline in prosaccade peak velocity may reflect either an increased rate of decay of the effect of the transient visual signal at the saccadic goal, or a failure of the continuing presence of the target to sustain neural activity in the saccadic system.

Adult↗

PubMed2004

Hemispheric specialization of the lateral prefrontal cortex for strategic processing during spatial and shape working memory.

OBJECTIVE: We investigated whether spatial working memory (WM) is associated with functional specialization of the right prefrontal cortex (PFC) relative to WM for shapes. We designed spatial and shape WM tasks that are relatively easy to perform and that minimize both task-switching and manipulation demands. The tasks use identical stimuli and require the same motor response. METHODS: We presented 12 subjects with target shapes that appeared in particular locations. Subjects maintained either the location or the shape of the targets in WM and responded to each probe by indicating whether it was a target. During a non-WM control task, subjects indicated whether the probe appeared on the right or left side of the screen. Subjects were scanned with a 3.0 T Siemens scanner and data were analyzed using SPM99. The WM tasks were compared to identify PFC activation that was different for spatial versus shape WM. Each WM task was also compared to the control task. RESULTS: compared with shape WM, spatial WM performance was faster and more accurate and was associated with increased right ventrolateral and frontopolar PFC activation. In contrast, compared to spatial WM, shape WM was associated with increased left ventrolateral PFC activity. CONCLUSIONS: These findings demonstrate hemispheric specialization for spatial versus shape WM in the ventrolateral PFC. The increased activity in the right PFC for spatial WM cannot be attributed to increased task difficulty, the stimuli used, or the response requirements. Rather, we propose that differences in performance and activation reflect the use of configural processing strategies for spatial WM.

Adult↗

PubMed2003

Identifying regional activity associated with temporally separated components of working memory using event-related functional MRI.

This study describes the neural circuitry underlying temporally separated components of working memory (WM) performance-stimulus encoding, maintenance of information during a delay, and the response to a probe. While other studies have applied event-related fMRI to separate epochs of WM tasks, this study differs in that it employs a methodology that does not make any a priori assumptions about the shape of the hemodynamic response (HDR). This is important because no one model of the HDR is valid across the range of activated brain regions and stimulus types. Systematic modeling inaccuracies may lead to the misattribution of activity to adjacent events. Twelve healthy subjects performed a numerical version of the Sternberg Item Recognition Paradigm adapted for rapid presentation event-related fMRI. This paradigm emphasized maintenance rather than manipulative WM processes and used a subcapacity WM load. WM trials with different delay lengths were compared to fixation. The HDR of the entire WM trial for each trial type was estimated using a finite impulse response (FIR). Regional activity associated with the Encode, Delay, and Probe epochs was identified using contrasts that were based on the FIR estimates and by examining the HDRs. Each epoch was associated with a distinct but overlapping pattern of regional activity. Activation of the dorsolateral prefrontal cortex, thalamus, and basal ganglia was exclusively associated with the probe. This suggests that frontostriatal neural circuitry participates in selecting an appropriate response based on the contents of WM.

Adult↗

PubMed2002

Schizophrenic subjects show deficient inhibition but intact task switching on saccadic tasks.

BACKGROUND: Schizophrenic patients have executive function deficits, presumably on the basis of prefrontal cortex dysfunction. Although they consistently show impaired inhibition, the evidence of a task switching deficit is less consistent and is often based on performance of neuropsychological tests that require several cognitive processes (e.g., the Wisconsin Card Sort Test [WCST]). We investigated inhibition and task switching using saccadic tasks to determine whether schizophrenic patients have selective impairments of these executive functions. METHODS: Sixteen normal and 21 schizophrenic subjects performed blocks of randomly mixed prosaccade and antisaccade trials. This gave rise to four trial types: prosaccades and antisaccades that were either repeated or switched. Response accuracy and latency were measured. Schizophrenic subjects also performed the WCST. RESULTS: Schizophrenic subjects showed abnormal antisaccade and WCST performance. In contrast, task switching was normal and unrelated to either antisaccade or WCST performance. CONCLUSIONS: The finding of intact task switching performance that is unrelated to other measures of executive function demonstrates selective rather than general impairments of executive functions in schizophrenia. The findings also suggest that abnormal WCST performance is unlikely to be a consequence of deficient task switching. We hypothesize that inhibition and task switching are mediated by distinct neural networks, only one of which is dysfunctional in schizophrenia.

Adult↗