Biomedical subjects

Britt Anderson

Publications and source records attributed to Britt Anderson.

7 recordsLinked to original sources

PubMed2006

Joint decoding of visual stimuli by IT neurons' spike counts is not improved by simultaneous recording.

Information about visual stimuli such as objects and faces is represented across populations of neurons of the inferior temporal cortex. Does recording from inferotemporal neurons simultaneously tell you more than recording from them sequentially? Equivalently, are neurons conditionally independent given a stimulus? To evaluate these issues, we recorded from two monkeys during a passive viewing task. Multiple neurons were simultaneously recorded on separate electrodes. From spike counts in 50-ms windows, we computed the mutual information between counts and images for each neuron individually and jointly with other simultaneously recorded neurons. To determine the significance of these values, we shuffled the stimulus labels (to test if there was significant information) or shuffled responses across trials involving the same image (to see if there was synergistic coding). We recorded from 127 pairs of neurons where each neuron individually was visually responsive. Depending on the time window, we found up to approximately 90% of these pairs showed significant information about the visual stimulus. Shuffling across trials failed to show evidence for synergistic coding. In summary, if you were given two of our neuronal responses and asked to guess the stimulus which produced them you could not, in principle, do better with two simultaneously recorded spike counts than with any two spike counts selected randomly from trials of the same type.

Algorithms↗

PubMed2006

Deficits in memory strategy use are related to verbal memory impairments in adolescents with schizophrenia-spectrum disorders.

OBJECTIVE: To assess the nature of learning and verbal memory deficits in adolescents with schizophrenia-spectrum disorders (SzS) (i.e., schizophrenia, schizoaffective disorder, and schizophreniform disorder). METHOD: Sixty patients with SzS (mean age=16.1 years, S.D. = 2.2) and 60 age- and gender-matched diagnosis-free healthy volunteers were assessed using the California Verbal Learning Test (CVLT). Planned analyses were conducted to assess the following aspects of memory: span of apprehension, verbal learning, short-term and long-term memory, rate of forgetting, interference, and organizational strategies. Adolescents with schizophrenia (Sz) were compared to those with schizoaffective disorder (SzA). Second, patients' test profiles were compared to those of controls. Relationships between initial learning and overall verbal learning with organizational strategy were explored. RESULTS: Neurocognitive profiles did not significantly differ between Sz and SzA participants. Patients performed significantly worse than healthy comparison subjects on measures of span of apprehension, verbal learning, short- and long-term memory, and organizational strategies after adjusting for differences in premorbid intelligence. No group differences were found in rate of forgetting or susceptibility to proactive or retroactive interference. CONCLUSIONS: Adolescents with SzS are characterized by significant verbal memory dysfunction similar to what has been observed in adults with first-episode schizophrenia. Deficits in consistency of learning over several trials, as well as a strong relationship between semantic organizational strategies and reduced learning capacity, implicate dysfunction of the dorsolateral prefrontal cortex as a contributor to verbal memory deficits in adolescents with SzS.

Adolescent↗

PubMed2006

A multielectrode study of the inferotemporal cortex in the monkey: effects of grouping on spike rates and synchrony.

We measured spiking activity from 175 pairs of visually selective neurons while a monkey performed a visual classification task in which the same image pairs appeared in informative and uninformative contexts. Spike counts and synchrony counts were higher during fixations of informative configurations. Spike field coherence showed low frequency (approximately 5-15 Hz) desynchronization when viewing informative stimulus configurations. Jitter statistics, which quantify synchrony and control for spike rates, showed less probable, more surprising patterns of synchronies when the monkey made the correct response than when he erred. Our results suggest that changes in spike counts parallel changes in raw synchrony counts and that both track aspects of stimulus context. Synchrony unexplained by rates changes, however, also occurs and correlates with performance.

Action Potentials↗

PubMed2006

XOR style tasks for testing visual object processing in monkeys.

Using visually complex stimuli, three monkeys learned visual exclusive-or (XOR) tasks that required detecting two way visual feature conjunctions. Monkeys with passive exposure to the test images, or prior experience, were quicker to acquire an XOR style task. Training on each pairwise comparison of the stimuli to be used in an XOR task provided nearly complete transfer when stimuli became intermingled in the full XOR task. Task mastery took longer, accuracy was lower, and response times were slower for conjunction stimuli. Rotating features of the XOR stimuli did not adversely effect recognition speed or accuracy.

Animals↗

PubMed2006

Declining medical decision-making capacity in mild AD: a two-year longitudinal study.

This is a report of a two-year longitudinal study comparing healthy older adult subjects (n = 15) and mild Alzheimer's disease (AD) patients (n = 20) using an objective performance measure of medical decision-making capacity (MDC). Capacity to consent to medical treatment was measured using the Capacity to Consent to Treatment Instrument (CCTI). The CCTI is a psychometric measure that tests MDC using a series of four core capacity standards: S1 (evidencing/communicating choice), S3 (appreciating consequences), S4 (providing rational reasons), and S5 (understanding treatment situation), and one experimental standard [S2] (making the reasonable treatment choice). For each standard, mild AD patients were assigned one of three capacity outcomes (capable, marginally capable, or incapable) based on cut-off scores derived from control group performance. At baseline, mild AD patients performed equivalently with controls on simple standards of evidencing a choice (S1) and making the reasonable choice ([S2]), but significantly below controls on complex standards of appreciation, reasoning, and understanding (S3, S4, and S5) (p < 0.02). Control performance was stable over time on all capacity standards. At one-year follow-up, the mild AD group did not show significant decline from baseline on any capacity standard. However, at two-year follow-up the mild AD group showed significant declines from baseline on the three complex standards (S3, S4, and S5) (p < 0.02), and a trend on one of the simple standards (S1). Over the two-year period, the proportion of marginally capable and incapable outcomes in the AD group increased substantially for four of the five standards (S1, S3, S4, and S5). Performance on [S2] remained stable over time in the AD group.We conclude that mild AD patients have impaired MDC at baseline, and demonstrate significant additional decline on complex consent abilities of appreciation, reasoning, and understanding over a two-year period. AD patients also show emerging impairment on the simple consent ability of evidencing choice at two-year follow-up. Capacity outcome data reflect similar declines over time for these four consent standards. The findings suggest the value of early assessment and regular monitoring at two-year intervals of MDC in patients with mild AD.

Aged↗

PubMed2006

Ethical and practical considerations in the management of incidental findings in pediatric MRI studies.

OBJECTIVE: The authors examined the ethical and practical management issues resulting from the detection of incidental abnormal findings on magnetic resonance imaging (MRI) research studies in healthy pediatric volunteers. METHOD: A retrospective examination of the findings from 60 clinical reports of research MRI scans from a cohort of healthy pediatric volunteers (ages 10-21) was conducted. RESULTS: A neuroradiologist noted incidental abnormalities in 8 (13%) of 60 subjects. Of these eight children, three (5%) adolescents were found to have abnormalities (possible tumor, possible vascular malformation, and unidentified bright object in white matter, respectively) that were judged to require further diagnostic workup. In the first two cases, follow-up MRI ruled out the possibility of a tumor or vascular malformation. In the third case, a follow-up MRI 24 months later found that the white matter abnormality remained stable and was thus deemed to be of no clinical significance. CONCLUSIONS: In healthy children who are participating in research MRI protocols, it is ethically difficult to determine whether films should be read clinically. Based on this retrospective analysis, there would have been no risk(s) associated with not reading the films. In contrast, considerable anxiety was generated as a consequence of having the scans clinically read by a neuroradiologist because of the reporting of incidental abnormalities that later turned out to be false positives. Also, the detection of no abnormality on a research-quality scan could imply erroneously to some subjects that no abnormality was present, which may have been falsely reassuring.

Adolescent↗

PubMed2005

Biases in attentional orientation and magnitude estimation explain crossover: neglect is a disorder of both.

Crossover refers to a pattern of performance on the line bisection test in which short lines are bisected on the side opposite the true center of long lines. Although most patients with spatial neglect demonstrate crossover, contemporary theories of neglect cannot explain it. In contrast, we show that blending the psychophysical construct of magnitude estimation with neglect theory not only explains crossover, but also addresses a quantitative feature of neglect that is independent of spatial deficits. We report a prospective validation study of the orientation/estimation hypothesis of crossover. Forty subjects (17 patients with and without neglect following unilateral brain injury and 23 normal controls) completed four experiments that examined crossover using line bisection, line bisection with cueing, and reproducing line lengths from both memory and a standard. Replicating earlier findings, all except one subject group exhibited crossover on the standard line bisection test, all groups showed a spontaneous preference to orient attention to one end of the lines, and all groups overestimated the length of short lines and underestimated long lines. Biases in attentional orientation and magnitude estimation are exaggerated in patients with neglect. The truly novel finding of this study occurred when, after removing the line from the bisection task, the direction of crossover was completely reversed in all subject groups depending on where attention was oriented. These findings are consistent with our hypothesis of crossover: (1) crossover is a normal component of performance on line bisection; (2) crossover results from the interplay of biases in attentional orientation and magnitude estimation; and (3) attentional orientation predicts the direction of crossover, whereas a disorder of magnitude estimation, not previously emphasized in neglect, accounts for the quantitative changes in length estimation that make crossover more obvious in neglect subjects. Paradoxically, we observed that the traditional line bisection test is suboptimal for exploring crossover because lines elicit spontaneous orientation responses from subjects that confound experimental manipulations of attention. We conclude that attentional orientation and magnitude estimation are necessary and sufficient to explain crossover and that bias in magnitude estimation is a core component of neglect.

Adult↗