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Biomedical subjects

B Crosson

Publications and source records attributed to B Crosson.

At least 37 records · Page 2Linked to original sources
PubMed1997

Resting and stimulated states in functional imaging studies: evidence of differences in attentional and intentional set.

In a [99mTc]-hexamethylpropyleneamine oxime single photon emission computed tomography study of cerebral blood flow (CBF) in a visual activation paradigm (awake, eyes closed versus eyes open viewing a reversing checkerboard pattern), the authors systematically measured previously observed qualitative alterations in frontal blood flow associated with visual stimulation (experiment 1). They confirmed a trend toward reductions in CBF throughout precentral cortex that approached significance in areas 9 and 46, in conjunction with significant increases in CBF in postcentral cortices, including visual association area PO, and areas 3-1-2, 22, and 23. The authors posited that these changes may be related to differences in attentional and intentional state in the eyes-closed and eyes-open conditions. Such differences should be associated with alterations in motor preparedness, leading to changes in response times and to alterations in thalamocortical gating of somatosensory information, which in turn lead to changes in somatosensory-evoked potential amplitudes. In experiment 2, the authors measured simple motor response times to a 1500-Hz tone stimulus and early components of somatosensory-evoked potentials under the same experimental conditions. In the visual stimulation condition, there was a significant increase in the evoked potential amplitude (t = 2.686, p = 0.021), and a significant decrease in response time (t = -2.464, p = 0.031). These observations provided tentative support for their hypothesis. The authors also demonstrated the major effect of normalization assumptions on regional blood flow measurements.

Adolescent↗
PubMed1994

Selective attention and aphasia in adults: preliminary findings.

Thirteen patients with left-hemisphere stroke and history of aphasia and 13 normal controls were administered the covert orientation of visual attention task (COVAT). This task presents targets to the right or left of a central fixation point after a cue (84% of trials) or with no cue (16% of trials). Left-hemisphere damaged patients also received tests of language function at the time of the study. For targets presented 100 msec after cue onset, normal controls demonstrated equivalent responding for targets to the left and to the right of a central fixation point. Patients with left-hemisphere damage showed slower reaction times when responding to targets on the right as opposed to the left side of space when attention was first cued to the opposite side of space (invalid trials) or when attention was focused on a central fixation point (uncued trials), but they did not show slower reaction times on the right side when attention was first cued to the right (valid trials). For left-sided targets, no differences between valid, invalid, and uncued trials existed. Slower responding to right- as opposed to left-sided targets on invalid and uncued trials was correlated with impaired performance on six of seven language measures for patients with left-hemisphere damage. Implications for the relationship between language and selective attention systems in the left hemisphere are discussed.

Adult↗
PubMed1994

A technique to localize activation in the human brain with technetium-99m-HMPAO SPECT: a validation study using visual stimulation.

UNLABELLED: This study extends and validates a system for localizing brain activity changes based on fiducial markers, coregistration of SPECT and MRI structural images and atlas/MRI-assisted localization. METHODS: Ten normal subjects underwent 99mTc-HMPAO SPECT during a resting eyes-closed baseline measurement and during visual stimulation (8-Hz reversing checkerboard). SPECT scans were registered with MRI scans obtained from each individual using a fiducial-based system that minimized z-axis and rotational errors, and registration was further refined along the x- and y-axes by superimposing corresponding axial SPECT and MRI slices. Regions of interest (ROIs) were located on MRI slices with the aid of an atlas. Corresponding loci on SPECT slices were chosen and incrementally adjusted such that the center of a ROI was located precisely at the maximum of activity in the visual cortex or the cortical gray matter ribbon. RESULTS: Activity in the calcarine cortex increased by 44.39% during visual stimulation (p < 0.001). Adjustment of ROI location in accordance with local activity maxima yielded superior results to a method relying strictly on atlas/MRI localization. Premotor cortex activity declined by 16.91% on the right (p < 0.01) and 13.85% on the left (p > 0.05), whereas no changes occurred in the somatosensory cortex. CONCLUSION: Changes in visual cortical activity were most comparable to previous functional MRI studies but also congruent with PET and SPECT findings. Using the locus of peak activity to aid in defining cortical ROIs improves the signal-to-noise ratio by reducing noise related to inevitable minor registration errors.

Adolescent↗
PubMed1988

California Verbal Learning Test (CVLT) performance in severely head-injured and neurologically normal adult males.

California Verbal Learning Test (CVLT) performance was compared for 33 head-injured and 33 neurologically normal adult males. On learning trials, head-injured persons recalled fewer items than controls in general, though the percent of improvement between trials did not differ for these groups. Head-injured patients also demonstrated more intrusions and used semantic groupings less than did normal controls during learning trials. On delayed recall trials, head-injured persons remembered a smaller percentage of items they had learned earlier than did controls. Semantic cues aided recall for head-injured but not normal persons. Head-injured persons were less able to discriminate list from nonlist items during the recognition trial. Results indicated both retrieval and storage (i.e., encoding or retention) deficits for the head-injured group. The CVLT is a useful instrument for defining memory deficits in a head-injured population.

Adult↗
PubMed1987

Role of the thalamus in language: is it related to schizophrenic thought disorder?

Crosson (1985) proposed a model for language production which integrated cortical with subcortical functions. The implications of this model for schizophrenia are explored. One conclusion is that neural systems, as opposed to a single neural focus, account for schizophrenic symptoms. In this light, data regarding dysfunction in the limbic system, nucleus accumbens, globus pallidus, and prefrontal cortex, which are often seen as contradictory, can be viewed as complementary. Another conclusion is that Crosson's model may have implications specific to schizophrenic thought disorder. Random triggering of semantic segments and inability to maintain contextual referents are discussed in the context of the language production theory.

Brain Mapping↗
PubMed1986

A case of thalamic aphasia with postmortem verification.

This study discusses a case of aphasia after dominant thalamic lesion, a hemorrhagic infarction. Unlike other such cases, both repeated standardized assessment and postmortem verification were available. The patient was assessed at 3 weeks and again at 9 weeks postonset. The aphasia demonstrated the syndrome common to dominant thalamic hemorrhage: fluent but paraphasic output sometimes deteriorating to jargon, comprehension less impaired than this type of output usually indicates, and the least impairment in repetition. As sometimes reported in previous cases, semantic paraphasias were more common than phonemic paraphasias. The lesion was located in the dorsal aspect of the lateral nucleus, but it extended into the pulvinar, including the anterior superior lateral aspect which has been implicated in language by previous studies. Thus, data from this case are consistent with an involvement of the dominant pulvinar in language and suggest that this role involves the semantic aspects of language.

Aged↗
PubMed1986

On localization versus systemic effects in alcoholic Korsakoff's syndrome: a comment on Butters (1985).

In a recent article, Butters (1985) emphasized that involvement of the nucleus basalis of Meynert may be the critical area affected in alcoholic Korsakoff's syndrome. Examination of the neuroanatomical pathways between this structure and other neural structures involved in memory (i.e., hippocampus and dorsal medial thalamus) suggests a somewhat different emphasis might be more productive in facilitating understanding of memory processes. The important question is: In what way might the nucleus basalis of Meynert interact with other structures involved in memory processes? Other data also suggest that it will be necessary to emphasize a whole system of brain structures as opposed to one or two small nuclei.

Alcohol Amnestic Disorder↗
PubMed1985

Memory span and long-term memory deficits in brain-impaired patients.

Measures of verbal and visuospatial memory span and long-term memory were obtained from 21 brain-impaired and 21 neurologically unimpaired Veterans Administration medical patients. Significant deficits in both memory span and long-term memory were observed in the brain-impaired patients. Contrary to predictions from the experimental literature, memory span tests that require more processing of item content and location were not superior in detecting the memory span deficits. Discriminant function analyses revealed that measures of verbal and visuospatial long-term memory provided unique discrimination between the brain-impaired and unimpaired patients. However, when memory span measures were analyzed alone, inclusion of more than one measure of memory span did not provide additional unique discrimination. Implications for the clinical assessment of memory functioning are discussed.

Brain Damage, Chronic↗
PubMed1985

Subcortical functions in language: a working model.

The current paper explains a model of subcortical language functions that focuses on dynamic interactions between the cortex, the thalamus, and the basal ganglia in the production of spoken language. The model was derived from (a) studies of subcortical lesions and language, (b) studies of subcortical stimulation and language, (c) knowledge regarding neural pathways between various cortical and subcortical structures, and (d) indications that preverbal monitoring of language occurs. In the current model, the thalamus plays roles in cortical arousal and activation and in preverbal semantic monitoring. The basal ganglia function to regulate the degree of excitation conveyed from the thalamus to the cortex and to time the release of formulated language for motor programming. Consistency with classical syndromes of aphasia and potential applications to other areas in the neurosciences are discussed. The current theory, unlike previous formulations, is specific enough that testable hypotheses can be derived.

Aphasia↗
PubMed1984

An individualized memory retraining program after closed-head injury: a single-case study.

A memory-retraining program was designed for a patient approximately 2 1/2 months after he suffered a closed-head injury. Tests showed his memory deficit to be relatively isolated in the verbal sphere. An attempt was made to design a program in which tasks resembled the environmental demands on the patient for retention of verbal material. On a routine basis, the patient was read various paragraphs and was subsequently required to write them from memory. Three different strategies were used in an attempt to improve memory. After 15 days of training, the patient improved from an impaired level of verbal recall to a normal level. Strategies employing (a) visual imagery and other mnemonic devices and (b) questioning during presentation appeared to be most effective in facilitating retention. There was some drop in memory performance at a 9 month follow-up, and the patient was encouraged to resume active use of mnemonic strategies. Implications for further study are discussed.

Adult↗
PubMed1981

Dichotic ear preference for C-V-C words in Wernicke's and Broca's aphasias.

A dichotic listening task was administered to subjects with a relatively distinct Broca's aphasia, subjects with a relatively distinct Wernicke's aphasia, and normal subjects. The dichotic stimuli consisted of C-V-C words differing in initial consonant only. Subjects were instructed to respond only to the stimulus of which they were most sure by pointing to a picture representing the dichotic stimuli or foils. while normal subjects demonstrated the usual right ear effect, both the Broca's and Wernicke's aphasia groups demonstrated left ear effects. One salient explanation for these results was that any severe defect in the language systems of the left hemisphere affects the way that the left hemisphere processes linguistic information. It was postulated that left ear stimuli, which arrive at the left hemisphere later, disrupt the processing of right ear stimuli in subjects with aphasia. However, a more definitive explanation requires further research.

Adult↗