1,721,052 research outputs found
Cholinergic enhancement and increased selectivity of perceptual processing during working memory
No full textUsing functional magnetic resonance imaging, we investigated the mechanism by which cholinergic enhancement improves working memory. We studied the effect of the cholinesterase inhibitor physostigmine on subcomponents of this complex function. Cholinergic enhancement increased the selectivity of neural responses in extrastriate cortices during visual working memory, particularly during encoding. It also increased the participation of ventral extrastriate cortex during memory maintenance and decreased the participation of anterior prefrontal cortex. These results indicate that cholinergic enhancement improves memory performance by augmenting the selectivity of perceptual processing during encoding, thereby simplifying processing demands during memory maintenance and reducing the need for prefrontal participation
Effects of cholinergic enhancement on brain activity during working memory: PET and fMRI studies in human subjects.
No full textSpatial and temporal distribution of face and object representation in the human brain
No full textThe research summarized here shows that cortical representations of faces and objects are
both spatially and temporally distributed. Category-related neural activity that is evoked by
visually presented faces and other objects appears to begin in extrastriate regions in ventral and
lateral occipitotemporal cortices. These early responses appear to reflect feedforward processes
that are not strongly modulated by the effects of memory and attention. Because hemodynamic
imaging is insensitive to these early category-related responses, their topography is not known in
detail, and, consequently, it is unknown if these early responses show the same local distribution
of overlapping representations as do the later responses. In monkeys, early responses in IT
cortex appear to carry more information about between category distinctions than about finer
within-category distinctions. The role of early responses in human face and object processing
may similarly be related more to coarser between-category discriminations. These early
between-category discriminations could initiate further processing that is relevant for the
identified category. After the early responses, further neural processing in extrastriate regions is
in concert with neural activity in other brain areas. Thus, the extended distribution of face and
object representations appears to be related to the later responses. The recruitment of the
extended distribution can serve to elaborate the information contained in the representation,
enable recognition of familiar faces and objects, and allow attention to modulate how the
representation develops. The locally distributed representations within extrastriate visual cortical
areas that are observed with neuroimaging reflect late neural responses in these areas that are
modulated by the influence of the extended distribution. The relationship between the local
distribution of early and late responses in extrastriate cortices is unknown, but single unit studies
in monkeys and recordings with intracranial electrodes indicate that they may be closely linked
Distinct, overlapping representations of faces and multiple categories of objects in ventral temporal cortex
No full textSelective Effects of Cholinergic Modulation on Task Performance during Selective Attention
No full textThe cholinergic neurotransmitter system is critically linked to cognitive functions including attention. The current studies were designed to evaluate the effect of a cholinergic agonist and an antagonist on performance during a selective visual attention task where the inherent salience of attended/unattended stimuli was modulated. Two randomized, placebo-controlled, crossover studies were performed, one (n=9) with the anticholinesterase physostigmine (1.0 mg/h), and the other (n=30) with the anticholinergic scopolamine (0.4 mc/kg). During the task, two double-exposure pictures of faces and houses were presented side by side. Subjects were cued to attend to either the face or the house component of the stimuli, and were instructed to perform a matching task with the two exemplars from the attended category. The cue changed every 4-7 trials to instruct subjects to shift attention from one stimulus component to the other. During placebo in both studies, reaction time (RT) associated ..
Reductions in parietal and temporal cerebral metabolic rates for glucose are not specific for Alzheimer's disease
No full textReduction in the regional cerebral metabolic rate for glucose (rCMRglc) in the parietal and temporal regions has been shown in Alzheimer's disease (AD). The specificity of these findings for this disease state is uncertain. We repeatedly measured rCMRglc with positron emission tomography and [18F]2-fluoro-2-deoxy-D-glucose in the resting state in a 68 year old man with slowly progressive dementia who, during life, was initially diagnosed as having dementia of the Alzheimer type, then Parkinson disease with dementia, but was found to have only Parkinson's disease at necropsy. Metabolic ratios (rCMRglc/mean grey CMRglc) were significantly (p < 0.05) reduced in parietal and temporal regions, as well as in the prefrontal and premotor areas. This pattern was similar in regional distribution and magnitude of the defect to that seen in patients with probable AD. These results suggest that reductions of glucose metabolism in association neocortex in AD are not specific to the disease process, but may be related to the dementia state
Seeing with one's hands: Supramodal cortical organization of perception in the human brain revealed by fMRI
No full textEffect of task difficulty on cerebral blood flow during perceptual matching of faces
No full textTo aid our understanding of age-related changes in brain activation during visuoperceptual processing, we designed an experiment to test the effect of task difficulty on regional cerebral blood flow (rCBF) as measured by positron emission tomography (PET). We report here the results from 10 young subjects engaged in match-to-sample tasks of progressively degraded faces. The tasks consisted of a control task, a face matching task with no stimulus degradation, and five levels of degradation: 20%, 40%, 50%, 60%, and 70%. Both performance accuracy and reaction times deteriorated significantly with increasing face degradation. There was a significant increase of rCBF in bilateral fusiform gyri during all face-matching conditions compared to the control task, and bilateral prefrontal activation during the 70% degradation condition. Linear regression analyses revealed a significant increase of rCBF in the right prefrontal cortex, and linear decreases of rCBF in the striate and fusiform cortex as face degradation increased. Performance on the 70% task was correlated positively with rCBF in right prefrontal and bilateral fusiform gyri, and negatively with left prefrontal and striate rCBF. These results show that the right prefrontal, striate, and ventral extrastriate cortex are the principal brain regions that modulate their activity as this visual discrimination task becomes more difficult. The right prefrontal increase probably represents an increasing demand on working memory or attention, whereas decreased rCBF in the striate cortex may be due to changes in the characteristics of the stimuli, or to suppression of low-level processing by one of a number of mechanisms. This experiment has implications both for the design of neuroimaging experiments, and for interpreting differences in rCBF activation between groups
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