Search PubMed⌕ Search

Biomedical subjects

D T Stuss

Publications and source records attributed to D T Stuss.

At least 55 records · Page 3Linked to original sources
PubMed1995

Concept generation: validation of a test of executive functioning in a normal aging population.

A new test, Concept Generation, was designed to fractionate the processes that underlie sorting performance in an efficient paper-and-pencil format. The test was administered to 60 subjects, aged 18-79. Results indicated age-related deficits for self-initiated concept formation, shifting set, output monitoring, and perseverative tendencies. When cuing was introduced to increase structure, age group differences were attenuated or eliminated. Within the older group, subgroups were identified based upon the nature of their repetitions. The hypothesis that sorting behavior is mediated by executive functions led to correlational analyses between Concept Generation scores and other measures of executive functioning. The pattern of correlations supported the construct validity of the Concept Generation test. In addition to providing preliminary evidence for the usefulness of Concept Generation in executive functioning assessment, the results replicated and extended previous work on executive functioning in older individuals.

Adolescent↗
PubMed1994

Neurobiology of conscious experience.

Recent research and theory suggest that conscious experience involves a modelling process. The human brain generates an internal model to fit incoming information about the external world, and experiences the model rather than the information. The modelling occurs at the level of the neocortex and may be associated with specific oscillatory field potentials. Imagining exercises the modelling system independently of sensory information. General disorders of consciousness are caused by damage to those areas of the brain that energize and direct the modelling process Specific deficits of consciousness are caused by focal lesions to sensory or motor cortex that prevent the modelling of particular input and output patterns.

Attention↗
PubMed1993

Capture errors and sequencing after frontal brain lesions.

This study addresses the effect of strong routine associations (capture errors) in hindering the control of on-line serial or sequencing tasks. Patients with focal frontal lobe lesions were significantly inferior to normal control subjects and patients with posterior brain lesions, when conditions that may lead to capture errors were present. The results suggest that the primary dysfunction exhibited by patients with frontal lobe lesions on capture error tasks may lie not in the disengagement from the invalid associations but in focusing attention to alternative strategies of response.

Adult↗
PubMed1993

The usefulness of CT scanning in diagnosing dementia of the Alzheimer type.

In order to determine the usefulness of Computerized Tomography (CT) scanning in making a diagnosis of dementia of the Alzheimer type, a group of patients diagnosed by NINCDS-ADRDA criteria (n = 22) were compared to a group of normal subjects (n = 49) using certain defined linear CT scan measurements. These measurements included specific measurements of the temporal lobes (temporal horns). Subjects were classified correctly 91.5% of the time with a high degree of probability. A diagnostic equation is presented which will allow testing of these methods in a prospective fashion.

Aged↗
PubMed1992

Perceptual closure and object identification: electrophysiological responses to incomplete pictures.

Event-related potentials were recorded during the naming of pictures of concrete objects. The pictures were presented at three levels of completeness: 10, 30, and 60%. The ERP waveforms were evaluated according to the level of picture completeness and the correctness of naming. A negative wave in the latency range of 250-550 ms was significantly more negative when the pictures were more incomplete, regardless of the correctness of response. This N400 wave is proposed as being related to hypotheses about the identity of the object. A late positive wave in the latency range of 550-650 ms followed the negativity, but only when the response was correct. This may reflect the subject's certainty about the perceptual analysis, a verification of the identity of the object. A slow parietal negativity lasting up to 2 sec was largest for the least complete picture. This therefore varied with the perceptual difficulty.

Adult↗
PubMed1992

Biological and psychological development of executive functions.

The purpose of this overview is to provide a background for understanding the relation between the biological maturation of the frontal lobes and the development of the psychological concept of executive functions. In the first section, an interactive hierarchical feedback model is presented as a heuristic way of conceptualizing the relationship of the frontal lobes and executive functions to other brain regions and abilities. The following two sections present a synopsis of research on biological maturation and the psychological development of executive functions.

Child↗
PubMed1992

"No longer Gage": frontal lobe dysfunction and emotional changes.

This review presents the multiple changes in emotional response and personality that occur after damage to the frontal systems, proposes operational definitions, and analyzes the published reports according to these definitions. Neurological causes of frontal lobe damage and associations of frontal dysfunction with psychiatric disturbances are summarized. It is concluded that symptoms of frontal lobe damage that have been labeled as emotional disturbances may be classified as disorders of drive or motivation, mood (subjective emotional experience), and affect (emotional expression). It is proposed that the primary change after frontal lobe pathology is a disorder of personality, a change in the stable response patterns that define an individual as a unique self. Dysfunction of personality includes cognitive abilities, with a disorder of self-reflective awareness as a key deficit.

Adult↗
PubMed1991

Assessment of competency: the role of neurobehavioral deficits.

We present a practical set of guidelines for assessing competency in patients with cognitive deficits due to neurologic disorders such as stroke, head injury, Alzheimer disease, and multi-infarct dementia. Our focus is the evaluation of cognitive processes underlying the ability to make competent decisions, with an emphasis on the identification of areas of preserved function that may be used to bypass intellectual deficits. The assessment of the cognitive processes underlying competency involves a series of steps designed to evaluate attention, language, memory, and frontal lobe function. The examiner must first show that the patient has an adequate level of attention for participation in the further testing of specific cognitive functions; second, that the patient is able to comprehend relevant instructions, retain information long enough to evaluate it in relation to relevant recent and remote experiences, and express his or her wishes; and finally, that the patient has sufficiently intact judgment and awareness. The examiner must determine whether the patient's preserved cognitive abilities are sufficient for him or her to make an adequate judgment in relation to the specific question being asked. If cognitive function is found to be significantly impaired, the examiner should do a detailed assessment for the presence of compensatory abilities that can be used to bypass the deficits. For example, the examiner should assess whether patients who cannot speak are still able to express their wishes by pointing, using gesture, or even by drawing pictures. Unless such an assessment has been done, patients should not be considered incompetent.

Attention↗
PubMed1990

Frontal lobe influences on delusions: a clinical perspective.

The presence of delusions, a significant feature of many schizophrenic patients, implies a disturbance of reality testing. Through descriptions of a number of organic delusion syndromes featuring frontal damage, and a theory of prefrontal functions, a correlation of schizophrenic delusions and prefrontal malfunctions is postulated.

Adult↗
PubMed1989

Frontal lobes and language.

Numerous theories discuss the neuropsychological functions of the frontal lobes, most based on some concept of supramodality, and an extensive literature presents the phenomenology and semiology of language and communication deficits after focal brain lesions involving the frontal lobes. Despite this, few attempts have been made to link the clinical phenomenology to a theory. This paper presents (1) a general theory of frontal functions; (2) a brief summary of experimental and anatomical literatures in support of defined frontal functional systems; (3) clinical observations that delineate these functional systems for the specific modalities of language and communication; (4) a review of the available literature supporting the idea of specific modal and supramodal language and communication capacities; (5) hypotheses about the distributed anatomy of these functional systems; and (6) implications for traditional clinical notions of aphasia, particularly in relation to a general theory of frontal lobe functions.

Aphasia↗
PubMed1989

Traumatic brain injury, aging and reaction time.

The effects of traumatic brain injury (TBI) and aging were compared on tests of simple and complex reaction time (RT). Simple RT was not significantly affected by aging or TBI. TBI patients, however, tended to be slower on Simple RT tasks, and had a larger standard deviation. Individuals over age 60 and patients of any age with TBI demonstrated slower RT with choice RT tests. In addition, both groups (those over 60 and TBI patients) were less able than other groups to inhibit the processing of redundant information. For the TBI patients, this occurred primarily on reassessment. These results suggest that the deficit in both aging and TBI is not only a generalized neuronal slowing but a more specific impairment in attentional control processes, exhibited as a deficit in focused attention.

Adolescent↗
PubMed1989

Reaction time after head injury: fatigue, divided and focused attention, and consistency of performance.

Three groups of patients who had suffered head injury were compared with matched control subjects on reaction time (RT) tasks. Group I consisted of outpatients previously hospitalised for head injury of wide ranging degrees of severity, assessed at varying intervals after injury. Group II was composed of non-hospitalised mildly concussed patients. Group III was made up of head injured patients of varying degrees of severity assessed 7-10 months after initial hospitalisation for their injury. The reaction time tests were graded in difficulty, from a simple RT response to a complex choice RT test. In addition, subjects were compared in their ability to ignore redundant information during one of the choice RT tests. The findings indicate that traumatic brain injury causes slower information processing, deficits in divided attention, an impairment of focused attention, and inconsistency of performance.

Adolescent↗
PubMed1988

Electrophysiological manifestations of typicality judgment.

Ten male subjects participated in an event-related potential study of typicality judgment of words that were of either high or low frequency of usage. The amplitude of a negative wave with an average peak latency of 490 msec (N400) correlated with the goodness-of-fit of a word to a particular category independent of frequency, with poor examples of the category evoking a significantly more negative waveform. The relative insensitivity of the N400 to word frequency suggests that the N400 reflects some postlexical evaluation rather than lexical access.

Adult↗
PubMed1988

Severe remote memory loss with minimal anterograde amnesia: a clinical note.

We describe a patient who presented with apparent human Klüver-Bucy syndrome. After pharmacological treatment, his problems gradually resolved, with the exception of some unconcern about this present situation, a mild naming and word list generation deficit, a severe remote memory loss and, in comparison, a minimal anterograde memory disturbance. He has been able to relearn certain details of his personal past. These relearned memories are independent of a sense of personal intimacy. The "relearned memory" was frequently associated with a memory of how and when the information had been reacquired. The results suggest that anterograde and retrograde memory functions may, in at least certain patients, be dissociable. The apparently absolute loss of personal memories indicates that either a retrieval deficit or storage depletion are plausible hypotheses of the remote memory loss in this patient.

Amnesia↗
PubMed1988

The neuropsychology of paramedian thalamic infarction.

A longitudinal study of three patients with CT-scan documented paramedian thalamic infarctions (bilateral, primarily right, unilateral left) is reported and the neuropsychology of human paramedian thalamic infarction is reviewed. The neuropsychological deficits following these selected lesions, the nature of the clinical memory disorder, and the neuroanatomy of memory are discussed. The significance of cortical/subcortical relationship in explaining observed behavioral changes is emphasized. Brain damage with maximum involvement in the dorsomedial nuclei and mamillothalamic tracts appears to cause primarily a memory disorder and frontal-limbic behavioral changes, the severity and profile of deficits depending on lesion extent and location. Both anterograde and remote memory loss may be present. Asymmetry in memory at the level of the thalamus was observed, following the left-verbal, right-nonverbal dichotomy.

Aged↗
PubMed1988

How long does it take to recover from a mild concussion?

Twenty-two adults with mild concussions were assessed 5 times during the first 3 months after injury. The initial tests were performed within 72 hours of injury. Each evaluation included a neurological examination and neuropsychological reaction time (RT) tests of simple and choice RT variations. The concussed subjects were compared with control subjects matched for age, sex, and education. The time of day of the testing was equated for the two groups. None of the concussed subjects had a significant neurological deficit and none was hospitalized. There was no significant difference in the number of errors by the two groups on the RT tests. On the simple RT test, requiring a predetermined response to a specific signal, there was no significant difference between the groups, although the concussed group was approximately 28 ms slower on the average than the control group. On the choice RT tests, however, which demand an increased amount of attention and information processing, the concussed subjects were significantly slower than the normal control group, especially during the 1st month after injury. Even after 3 months, the concussed subjects had not yet attained the skill of the control group. Analysis of the response curves over time suggested two processes: an improvement in the concussed group and a slowing in the control group. Within the concussed group, there was no correlation of RT with the severity of the concussion. Even mild concussions can cause significant attentional and information processing impairment in the absence of any apparent neurological problems. Specific neuropsychological tests are necessary to reveal the deficit. A significant impairment seems to last for several weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Evaluation of information-processing speed and neuropsychological functioning in patients with myotonic dystrophy.

Patients with myotonic dystrophy (MD) were compared to a control group, matched to the patients in important demographic variables including IQ, on the Sternberg Memory Scanning procedure, to investigate the hypothesis of a selective change in speed of information processing in MD patients. The neuropsychological functioning of these MD patients was also compared to normative data to provide a descriptive picture of their abilities; these results were correlated to the factors of age of onset and duration of the disease. Finally, the MD patients were also compared to the defined control group on the neuropsychological measures. There was little evidence of selective slowness of information processing or particular deficit independent of overall IQ. Neuropsychologically, the MD patients as a group performed at the low average level. There was, however, a wide range of abilities, suggesting that MD patients are not a unitary group in terms of neuropsychological functioning. Age of onset of the disease was important, at least for certain results. Further research of the neuropsychological functioning of MD patients must account for the wide range of results, with more precise measures of actual onset of the disease and muscular weakness, in a longitudinal evaluation.

Attention↗