Showing papers by "Michael P. Alexander published in 2003"

Staying on the job: the frontal lobes control individual performance variability.

Abstract: The causes of variability of performance by individual subjects have rarely been investigated, although excessive variability or inconsistency may be a functionally significant factor for many real-life activities. Our objective was to determine whether patients with focal frontal brain lesions have excessive individual performance variability. Thirty-six patients with focal frontal (n=25) or non-frontal (n=11) lesions were compared with 12 control subjects on different measures of intra-individual variability: dispersion within a testing session; and consistency across testing sessions. Four reaction time tasks, varying in levels of complexity and based on a model of detection using feature integration, were administered. Following the first test session, 22 patients and 10 controls returned for two subsequent test sessions, which permitted the assessment of consistency of performance. Measures of abnormal dispersion of performance on these tests were observed in frontal patients only (except those with exclusively inferior medial damage). Disturbances in consistency of performance were observed primarily in patients with frontal lesions. Damage to the frontal lobes impairs the stability of cognitive performance. Damage to different frontal regions causes different profiles of abnormal variability. Fluctuations in performance of a task may underlie some of the reported difficulties in daily tasks reported by patients with frontal injuries.

California Verbal Learning Test: performance by patients with focal frontal and non-frontal lesions.

Abstract: Although frontal lobe lesions do not cause classic amnesia, they may disrupt learning and memory in a number of ways. To investigate in finer detail the regions of frontal injury that are associated with impaired learning and to define the cognitive processing deficits specific to each region that disrupt memory, we compared 33 patients with focal frontal injury with patients with non-frontal injury and with normal controls on a standard neuropsychological instrument, the California Verbal Learning Test (CVLT). Subgroups of patients with distinct lesion site profiles were compared in a number of learning measures. All of the subgroups of patients with frontal lesions (with one exception) had inefficient learning due to poor implementation of a strategy of subjective organization. Despite this organizational deficiency, the performance of patients with frontopolar lesions normalized across trials. Only the subgroups with lesions centred either on the left posterior dorsolateral frontal region or the posterior medial frontal region had overall impaired learning and recall. The left posterior dorsolateral frontal group was most significantly impaired on all measures. This recall impairment was secondary to a mild lexical-semantic deficit. A recognition memory deficit in the same group was due to an abnormal response bias. Several groups had a modest increase in perseverative recalls; the underlying mechanisms differed. Disruption of different cognitive processes associated with specific frontal regions underlies the varied patterns of memory impairment. This study has demonstrated even finer differentiations within the frontal region than previously known.

An outcome study of riluzole in amyotrophic lateral sclerosis--a population-based study in Ireland, 1996-2000.

Abstract: Riluzole is the only therapy proven in clinical trials to prolong amyotrophic lateral sclerosis (ALS) survival (approximately three months) Questions remain concerning riluzole's effectiveness in everyday practice, the appropriate duration of treatment, which certain subtypes of ALS specifically benefit from the medication, and whether early administration prolongs survival in ALS patients We report the results of a population-based outcome study of riluzole in the Irish ALS population over a five-year period Using data from the Irish ALS Register, we examined the survival of patients diagnosed with ALS between 1 January 1996 and 31 December 2000 who attended a general neurology clinic (n = 264 patients, MD = 16) An intention to treat analysis is employed 149 (61 %) patients were prescribed riluzole and the remaining 99 (39 %) were not Riluzole therapy reduced mortality rate by 23 % and 15 % at 6 and 12 months respectively and prolonged survival by approximately four months This beneficial effect was lost in prolonged follow-up Suspected or possible ALS patients receiving riluzole experienced similar improvement in survival as the overall cohort Survival benefit was more marked among patients with bulbar-onset disease Multivariate analysis did not show riluzole to be an independent predictor of survival We conclude that riluzole therapy improves ALS survival in everyday clinical practice by a short period of time This beneficial effect is transient and stopping the medication in advanced ALS should be reconsidered Bulbar-onset patients appear to particularly benefit from riluzole for unclear reasons Our initial observations support riluzole use in early ALS

Differential impairment of person-specific knowledge in a patient with semantic dementia

Abstract: We report the case of ST, a 61-year-old gentleman of superior intelligence, who presented with a five-year history of slowly progressive word finding difficulty for proper names. MRI (magnetic resonance imaging) showed marked atrophy in the left anterior temporal lobe and SPECT (single photon emission computed tomography) demonstrated hypoperfusion in the left anterior and inferior temporal region. A detailed behavioral analysis of the integrity of his semantic system revealed naming deficits for both proper and common names. ST also showed severe impairments in person-specific semantic knowledge, but preservation of knowledge for famous places and common objects. ST's semantic knowledge deficit for people emerged whether he was tested with the faces or the names of famous individuals. Variables that affect name retrieval, such as familiarity, age of acquisition, and frequency of concept encounter, do not account for the selective impairment of person-specific knowledge evidenced by ST. Qualitative differences between the nature of knowledge representations for people and for common objects may underlie this effect. Disruptions in left temporal regions associated with semantic processing may be sufficient to produce a selective deficit in person-specific knowledge.

Respiratory Management of Pediatric Patients with Spinal Cord Injuries: Retrospective Review of the duPont Experience:

Abstract: Pulmonary complications contribute to morbidity and mortality in spinal cord injuries (SCIs). A retrospective review of 20 years of experience with tracheostomy- and ventilator-dependent SCI children is presented. The authors developed and analyzed a database of 47 children (average age = 11.4 years). Of the patients, 27% had concomitant brain injuries, 6% had prior histories of reactive airway disease, and 2% had thoracic fractures. Injuries were caused by motor vehicle accidents (53%); gunshot wounds (19%); sports-related accidents (19%); and vascular injuries, transverse myelitis, or spinal tumors (8%). Of the injuries, 52% were high level (C1 to C2) and 48% were mid- or low level (C3 to C5). Two groups were analyzed for demographic information. Complications included tracheitis, atelectasis, and pneumonia. Mean tidal volume was 14 cm2/kg (maximum = 22 cm2/kg). Bedside lung function parameters were attempted to assess readiness and the rapidity of weans. T-piece sprints were used to successfully wean 63% of patients. Successfully weaned patients were compared with those not weaned. No deaths or readmissions for late-onset respiratory failure postwean occurred. The authors' clinical impression favors higher tidal volumes and aggressive bronchial hygiene to minimize pulmonary complications and enhance weaning. Successfully weaned patients had fewer complications. A critical pathway for respiratory management of SCI children is presented.

The evidence for brain injury in whiplash injuries.

Abstract: The evidence that brain damage can occur in injuries that produce whiplash is reviewed. The clinical phenomena for the two injuries are the same. Pure whiplash injury implies no, or minimal head contact, but many patients also have head contact against a head rest or the steering wheel or windshield. The relative severity of the neck injury and the head injury distinguishes whiplash from mild closed head injury. If there is brain injury is some patients with whiplash, it, by definition, falls at the mildest end of the concussion spectrum. The relationship between these two injuries is examined.

Is the Anterior Attentional System as Complex as the Posterior Attentional System

Abstract: The objectives of this review paper were to demonstrate whether there are separable attentional processes related to the frontal lobes, and to illustrate procedures on how to examine this question. Distinctions among frontal lobe attentional processes can be achieved if cognitive processes are adequately differentiated and if a sufficient number of patients are assessed to allow investigation of the relation of these distinct processes to different frontal lobe regions. The first section summarizes early evidence for the fractionation of the anterior attentional system using clinical tests. The second section extends these findings using experimental tests such as feature integration reaction time tasks. Different attentional processes include activation, task setting, shifting, and differentiating among relevant and irrelevant information. Although there are multiple anterior attentional processes related to different frontal brain regions, such anterior attentional processes likely interact wi...