Biomedical subjects

C L Wiggs

Publications and source records attributed to C L Wiggs.

11 recordsLinked to original sources

PubMed1999

Neural correlates of semantic and episodic memory retrieval.

To investigate the functional neuroanatomy associated with retrieving semantic and episodic memories, we measured changes in regional cerebral blood flow (rCBF) with positron emission tomography (PET) while subjects generated single word responses to achromatic line drawings of objects. During separate scans, subjects either named each object, retrieved a commonly associated color of each object (semantic condition), or recalled a previously studied uncommon color of each object (episodic condition). Subjects were also scanned while staring at visual noise patterns to provide a low level perceptual baseline. Relative to the low level baseline, all three conditions revealed bilateral activations of posterior regions of the temporal lobes, cerebellum, and left lateralized activations in frontal regions. Retrieving semantic information, as compared to object naming, activated left inferior temporal, left superior parietal, and left frontal cortices. In addition, small regions of right frontal cortex were activated. Retrieving episodic information, as compared to object naming, activated bilateral medial parietal cortex, bilateral retrosplenial cortex, right frontal cortex, thalamus, and cerebellum. Direct comparison of the semantic and episodic conditions revealed bilateral activation in temporal and frontal lobes in the semantic task (left greater than right), and activation in medial parietal cortex, retrosplenial cortex, thalamus, and cerebellum (but not right frontal regions) in the episodic task. These results support the assertion that distinct neural structures mediate semantic and episodic memory retrieval. However, they also raise questions regarding the specific roles of left temporal and right frontal cortices during episodic memory retrieval, in particular.

Adult↗

PubMed1998

Properties and mechanisms of perceptual priming.

Recent evidence suggests that the behavioral phenomenon of perceptual priming and the physiological finding of decreased neural responses with item repetition have similar properties. Both the behavioral and neurophysiological effects show graded changes with multiple repetition, are resistant to manipulations of particular stimulus attributes (e.g. size and location), and occur independently of awareness. These and other recent findings (e.g. from functional brain imaging in humans) suggest that perceptual priming may be mediated by decreased neural responses associated with perceptual learning.

Brain Mapping↗

PubMed1997

Modulation of human medial temporal lobe activity by form, meaning, and experience.

Clinically, the hallmark of the human amnesic syndrome is an impaired ability to consciously recollect or remember daily events. If the medial region of the temporal lobes, including the hippocampus and related structures, is critical for establishing these new memories, then this brain region should be active whenever events are experienced, regardless of whether subjects are asked explicitly to learn and remember. Here we show that the medial temporal region is active during encoding and that the hemisphere activated and the amount of activation depend on the type of stimulus presented (objects or words), whether the stimulus can be encoded for meaning (real objects and words versus nonsense objects and words), and task experience (first versus the second time a task is performed). These findings demonstrate that the medial temporal lobe memory system is engaged automatically when we attend to a perceptual event and that the location and amount of activation depend on stimulus characteristics (physical form, meaning) and experience.

Adult↗

PubMed1997

Monitoring frequency of occurrence without awareness: evidence from patients with Alzheimer's disease.

People are surprisingly accurate at judging how often an event occurs. Patients with Alzheimer's disease (AD), however, perform poorly on such tasks, suggesting that this ability is compromised when episodic memory is impaired. The tasks used to assess this ability in previous studies, however, placed demands on retrieval that could obscure whether frequency of occurrence was adequately encoded. We developed an indirect test of frequency monitoring based on changes in reading time as a function of item repetition. Using this procedure, patients with AD showed normal frequency monitoring for novel information (Turkish words) even though they were unable to remember the words or judge how often individual words had been presented. These findings suggest the existence of a mechanism that automatically monitors frequency of occurrence and operates outside of conscious awareness.

Aged↗

PubMed1996

Neural correlates of category-specific knowledge.

An intriguing and puzzling consequence of damage to the human brain is selective loss of knowledge about a specific category of objects. One patient may be unable to identify or name living things, whereas another may have selective difficulty identifying man-made objects. To investigate the neural correlates of this remarkable dissociation, we used positron emission tomography to map regions of the normal brain that are associated with naming animals and tools. We found that naming pictures of animals and tools was associated with bilateral activation of the ventral temporal lobes and Broca's area. In addition, naming animals selectively activated the left medial occipital lobe--a region involved in the earliest stages of visual processing. In contrast, naming tools selectively activated a left premotor area also activated by imagined hand movements, and an area in the left middle temporal gyrus also activated by the generation of action words. Thus the brain regions active during object identification are dependent, in part, on the intrinsic properties of the object presented.

Brain↗

PubMed1996

Hypervigilance in patients with obsessive-compulsive disorder.

The hypothesis that patients with obsessive-compulsive disorder (OCD) suffer from hypervigilant attention was investigated via explicit memory (incidental recall and recognition) and priming (reading speed) measures. OCD patients did not differ from normal controls on explicit measures of memory; specifically, recognition of unusual words (experiment 1) and recall and recognition of words and feature-specific information (experiment 2). Although both normal controls and OCD patients showed priming, the pattern of priming differed for the two groups (experiment 2). Specifically, patients with OCD failed to show feature-specific priming, suggesting they may have attended more focally on the priming task than did normal controls. These findings support previous reports of normal performance in OCD on explicit memory tasks, but suggest more sensitive measures may reflect differences in processing information.

Adult↗

PubMed1995

Discrete cortical regions associated with knowledge of color and knowledge of action.

The areas of the brain that mediate knowledge about objects were investigated by measuring changes in regional cerebral blood flow (rCBF) using positron emission tomography (PET). Subjects generated words denoting colors and actions associated with static, achromatic line drawings of objects in one experiment, and with the written names of objects in a second experiment. In both studies, generation of color words selectively activated a region in the ventral temporal lobe just anterior to the area involved in the perception of color, whereas generation of action words activated a region in the middle temporal gyrus just anterior to the area involved in the perception of motion. These data suggest that object knowledge is organized as a distributed system in which the attributes of an object are stored close to the regions of the cortex that mediate perception of those attributes.

Adult↗

PubMed1995

Working memory as assessed by subject-ordered tasks in patients with obsessive-compulsive disorder.

We tested patients with obsessive-compulsive disorder (OCD) and normal subjects (n = 18 per group) on a self-paced, working memory task that, based on studies of patients with focal brain lesions and functional brain imaging studies of normals, is largely mediated by prefrontal cortex. The OCD patients had normal working memory spans and normal recognition memory for all types of material tested (abstract words, common objects, and novel nonsense objects). The patients, however, were slow (p < .005), and the time they took to complete the tasks was significantly correlated with ratings of OCD symptoms (r = .539, p < .05) and depression (r = .643, p < .01), but not anxiety. Slowed performance on this self-paced task was discussed in relation to normal response times by OCD patients under typical laboratory conditions. It was suggested that this discrepancy may be related to a broader dissociation between real-world and laboratory performance as seen in some patients with prefrontal lobe dysfunction.

Adult↗

PubMed1994

Word retrieval to letter and semantic cues: a double dissociation in normal subjects using interference tasks.

Recent evidence suggests that letter and semantic category verbal fluency tasks may use different component processes of a distributed word retrieval system. We hypothesized that the retrieval of words that begin with the same letter places greater demands on frontal lobe mediated strategic search processes than on temporal lobe mediated semantic knowledge. Conversely, generation of words from the same semantic category places greater demands on semantic knowledge than on strategic search. This hypothesis was tested by requiring subjects to generate lists of words to letter and semantic cues alone and while performing an interference task. A motor sequencing task (developed by Moscovitch, Neuropsychology of Memory, pp. 5-22, 1992) was used to activate frontal regions and an object decision task was used to activate posterior temporal cortex. In support of the hypothesis, letter fluency was reduced to a greater extent by concurrent performance of the motor sequencing task than by the object decision task. The opposite interference pattern was found for semantic category fluency.

Adult↗

PubMed1994

Aging and feature-specific priming of familiar and novel stimuli.

English and Turkish words in 2 fonts were presented to young and elderly Ss, and memory was assessed directly with recognition tests and indirectly with reading time. Young and elderly Ss showed repetition priming on English words and showed larger priming effects when the study and test fonts were the same rather than different. Elderly Ss were impaired, however, on recognition of feature-specific information in comparison with young Ss. When Turkish words were shown, only young Ss evidenced priming, despite recognition performance above chance for both young and elderly Ss. A 2nd experiment replicated these findings with different materials.

Adolescent↗

PubMed1993

Aging and memory for frequency of occurrence of novel, visual stimuli: direct and indirect measures.

Memory for frequency of occurrence typically is investigated using familiar stimuli (e.g., words) and with "direct" tests of memory; that is, the subject is required to state explicitly how often an item occurred or which item occurred more often. Experiments 1 and 2 examined the effects of age on the ability to make judgments (i.e., direct tests) regarding the frequency of occurrence of words and of novel, visual stimuli (Japanese ideograms). In Experiment 3, young and old subjects were compared on "indirect" measures of memory for frequency of occurrence of these ideograms, as indexed by the mere exposure effect. On the direct test of memory, elderly and young subjects did not differ when shown words, but elderly were impaired compared with young subjects when ideograms were presented. When tested indirectly, both groups were sensitive to the frequency of occurrence of ideograms. The pattern of results replicates and extends previous findings regarding performance dissociations between direct and indirect measures of memory in aging.

Adolescent↗