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Biomedical subjects

M P Alexander

Publications and source records attributed to M P Alexander.

At least 19 recordsLinked to original sources
PubMed2005

Impaired concentration due to frontal lobe damage from two distinct lesion sites.

BACKGROUND: Investigations of cognitive deficits after frontal lobe damage have commonly relied on multidimensional tests and relatively coarse specification of lesion anatomy. Some form of impairment in attention is often asserted to cause the revealed deficits. OBJECTIVE: To describe a disorder of attention in patients with frontal damage using a theoretical model of the fundamental cognitive processes that underlie attention. METHODS: The ability to perform a task of concentrated responding was studied in 43 patients with well-defined chronic frontal lesions and 38 control subjects using a continuous reaction time (RT) test. Performance measures were mean RT, RT across blocks of the test, and errors. Lesion measures were coarse localization and a hot-spot analysis to detect finer grained lesion effects. RESULTS: Only patients with lesions in the right superomedial (SM) frontal regions had significantly prolonged RT consistently across the entire test. The critical lesion was in Brodmann's areas 24, 32, 9, and 46 days and in the adjacent corpus callosum. Patients with lesions in left lateral frontal (LL) regions made significantly more errors on the 20% of trials in the first block. The critical lesion was in areas 44, 45, and 47/12. CONCLUSION: Concentrating attention to respond is affected by lesions in two different frontal regions for reasons that reflect impairments in different cognitive processes. Right superomedial lesions cause an insufficient energizing of attention to respond. Left lateral lesions cause defective setting of specific stimulus-response contingencies. Constrained tests of attention can demonstrate impairments in specific cognitive operations following lesions to different regions of the frontal lobes.

Adult↗
PubMed2004

MEG analysis of "theory of mind" in emotional vignettes comprehension.

OBJECTIVE: Several studies suggested that an impaired "theory of mind" might play a key role in psychiatric disorders, such as autism and schizophrenia. Medial frontal lobe lesions of the right frontal lobe were reported to impair this ability. The aim of our study was to locate areas of the brain associated with the process of "theory of mind" in normal subjects. METHODS: In order to index the activity of brain areas related to "theory of mind" reasoning in sixteen normal adults, we administered an emotional ("happy", "sad", "angry" and "neutral") vignettes comprehension task during magnetoencephalography (MEG) recordings and analyzed these data by using SAM (synthetic aperture magnetometry), SPM99 and the permutation method. Subjects were presented with eight different videotaped social situations (each emotion has two vignettes) and were asked to indicate which emotion they represented. RESULTS: Statistically significant activation in the comparison of "happy"-"sad" and "angry"-"sad" was observed in the bilateral medial prefrontal cortices in the alpha frequency band. There were no significant differences in comparisons of each type of emotional vignette to the neutral vignettes, "happy"-"angry" comparison, and male-female comparisons. There was no significant difference in other frequency bands. CONCLUSION: This result suggests that bilateral medial prefrontal cortex are involved in the comprehension of emotional states of others.

Adult↗
PubMed2004

The neurological and cognitive sequelae of cardiac arrest.

BACKGROUND: Although cardiac arrest (CA) is commonly cited as a cause of amnesia, patients referred to the authors' center with a diagnosis of "amnesia" after CA rarely have isolated memory deficits. OBJECTIVE: To determine whether CA is a cause of pure amnesia and to assess patterns of cognitive deficits after CA. METHODS: The authors used cognitive assessment of 11 consecutive patients referred for memory deficits after CA, targeted at deficit domains identified in the literature reviews, and analysis of specific case reports and prospective studies of cognition after CA. RESULTS: The most common pattern of impairment in their patients was a combination of memory and motor deficits with variable executive impairment. No patient had isolated memory impairment. The case reports do not support the claim that isolated amnesia is a residual of CA; most cases of isolated amnesia are caused by subacute episodes of anoxia or excitotoxic injury. The prospective reports identify highly variable patterns of impairment, but isolated amnesia remains rare. CONCLUSIONS: Diffuse, sudden ischemic-hypoxic injury caused by cardiac arrest (CA) does not preferentially damage memory systems. Subacute or stepwise hypoxic or excitotoxic injury may cause isolated hippocampal injury and amnesia. The common pattern of impairment in the postacute phase after CA is a combination of memory, subtle motor, and variable executive deficits.

Adolescent↗
PubMed2003

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

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.

Cerebrovascular Disorders↗
PubMed2002

Age-related differences in movement representation.

Repetitive movements have been used as motor activation tasks in the investigation of various neurological disorders. To determine the importance of an age-matched control group in such studies we investigated whether there are significant age-related changes in the pattern of cortical activation seen during simple repetitive movements. Sixteen right-handed healthy subjects were studied-8 young and 8 old. Functional magnetic resonance images were acquired while subjects performed a motor task or a nonmovement rest condition. Two continuous motor tasks, index finger abduction/adduction and wrist extension/flexion, were performed by each hand, paced using a metronome. The fMRI data were processed and analyzed with SPM '99. For the between-group comparisons, for each motor task, contralateral primary sensorimotor cortex and premotor cortex had significantly greater activation in the Young group and caudal supplementary motor area had significantly greater activation in the Old group. Ipsilateral sensorimotor cortex was more significantly activated in the Old group for index finger motor tasks of both hands. All noted differences in the Old group were more prominent for the index finger movement and most prominent when using the nondominant hand. In conclusion, there are significant age-related differences in the activation pattern associated with repetitive movements. This may represent compensatory recruitment of motor cortical units in the older subjects as larger differences are noted in the older group during the more difficult motor tasks, those of isolated finger movement and nondominant hand use. This study has important implications for functional imaging experiments of neurological disorders in older subjects.

Adult↗
PubMed2002

Triangular backgrounds shift the bias of line bisection performance in hemispatial neglect.

OBJECTIVE: Patients with left neglect on line bisection show normal implicit sensitivity to manipulations of both the stimulus and the visual background. Three experiments were designed to define this sensitivity more exactly. METHODS: Normal controls and patients with left neglect performed a series of horizontal line bisection tasks. Independent variables were the configurations of the backgrounds for the line-rectangle, square, circle, left and right pointing isosceles triangles-and whether the background was the shape of the piece of paper or an outline drawn on a standard piece of paper. In a separate experiment different components of the triangle were outlined on a piece of paper. Deviation from true midpoint was calculated. RESULTS: Simply placing the target lines in a symmetric background such as a square or circle did not reliably reduce neglect. A triangle asymmetric in the horizontal plane caused a shift in bisection away from the triangle's vertex. With right pointing triangles the perceived midpoint shifted to the left of true centre (crossed over). The effects of the triangles were comparable in the patients and the controls when controlled for baseline bisection bias. The critical components of the triangles were the angular legs. This effect of background was not influenced by lesion site or by hemianopia. CONCLUSIONS: Patients with left visual neglect remain sensitive to covert manipulations of the visual background that implicitly shift the perceived midpoint of a horizontal line. This effect is strong enough to eliminate neglect on a bisection task. The mechanism of this effect is expressed through preattentive visual capacities.

Aged↗
PubMed2001

Stroop performance in focal lesion patients: dissociation of processes and frontal lobe lesion location.

There were three primary objectives: to examine the usefulness of the Stroop interference effect as a measure of frontal lobe function; to investigate the possibility of distinct lesion effects for word reading or color naming; and to specifically determine the brain regions necessary for the performance of the incongruent condition. Fifty-one patients with single focal brain lesions in frontal and non-frontal regions and 26 normal control subjects (CTL) were administered the word reading, color naming and incongruent conditions of the Stroop task. Only frontal lesions produced significant impairment. Patients with posterior lesions were not significantly deficient in any condition. Damage to the left dorsolateral frontal lobe resulted in increased errors and slowness in response speed for color naming. Contrary to Perret (Neuropsychology, 1974; 12: 323-330), lesions of the left frontal lobe did not result in a selective interference deficit on the Stroop incongruent condition. Rather, bilateral superior medial frontal damage was associated with increased errors and slowness in response time for the incongruent condition. This result is interpreted as failure of maintenance of consistent activation of the intended response in the incongruent Stroop condition. The results and conclusion are compatible with the prevalent theories of both the Stroop effect and the role of the superior medial frontal regions. The role of the anterior cingulate cortex on performance of the Stroop task is likely related to task and patient context.

Adult↗
PubMed2001

The frontal lobes are necessary for 'theory of mind'.

Patients with limited focal frontal and nonfrontal lesions were tested for visual perspective taking and detecting deception. Frontal lobe lesions impaired the ability to infer mental states in others, with dissociation of performance within the frontal lobes. Lesions throughout the frontal lobe, with some suggestion of a more important role for the right frontal lobe, were associated with impaired visual perspective taking. Medial frontal lesions, particularly right ventral, impaired detection of deception. The former may require cognitive processes of the lateral and superior medial frontal regions, the latter affective connections of the ventral medial frontal with amygdala and other limbic regions.

Brain Mapping↗
PubMed2001

What are preschool children eating? A review of dietary assessment.

Accurate assessment of dietary intake among preschool-aged children is important for clinical care and research, for nutrition monitoring and evaluating nutrition interventions, and for epidemiologic research. We identified 25 studies published between January 1976 and August 2000 that evaluated the validity of food recalls (n = 12), food frequency questionnaires (n = 9), food records (n = 2), or other methods (n = 2). We identified four studies that evaluated the reproducibility of food frequency questionnaires. Validity studies varied in validation standard and study design, making comparisons between studies difficult. In general, food frequency questionnaires overestimated total energy intake and were better at ranking, than quantifying, nutrient intake. Compared with the validation standard, food recalls both overestimated and underestimated energy intake. When choosing a method to estimate diet, both purpose of the assessment and practicality of the method must be considered, in addition to the validity and reproducibility reported in the scientific literature.

Child Nutritional Physiological Phenomena↗
PubMed2001

Chronic akinetic mutism after mesencephalic-diencephalic infarction: remediated with dopaminergic medications.

OBJECTIVE: Akinetic mutism (AKM) is an uncommon disorder with a complex neuropathology. There is no generally accepted treatment, and it is not known if late treatments are effective. The relationship between AKM and abulia is uncertain. METHODS: The effects of dopaminergic treatment of a patient with chronic AKM after discrete bilateral infarctions of the mesencephalic ventral tegmental area and the lateral hypothalamus were studied with motor measures, the Functional Independence Measure (FIM), and neuropsychological tests. RESULTS: Treatment with a combination of carbidopa/levodopa and pergolide produced prompt amelioration of AKM with dramatic and rapid improvement in FIM. An apathetic, amotivational state persisted despite resolution of akinesia and normal frontal executive functions. CONCLUSIONS: AKM may respond to dopaminergic treatment even after months of severe akinesia. The mechanism of abulia is more complex than simply a partial dopaminergic deficiency state and may persist even when AKM is treated and frontal cognitive functions are normal.

Adult↗
PubMed2001

The Trail Making Test: a study in focal lesion patients.

The relationship of the Trail Making Test (TMT) to the frontal lobes was tested by comparing patients with damage to the frontal and nonfrontal regions to control participants. Although the analysis of time measurements, both raw and transformed, showed notable slowing of frontal groups, error analysis proved to be a more useful method of categorizing performance. Analysis of errors on Part B indicated that all patients who made more than 1 error had frontal lesions. Dividing the frontal damaged patients into subgroups on the basis of the number of errors yielded specificity of brain-behavior relations within the frontal lobes. Patients with damage in dorsolateral frontal areas were most impaired. Those with inferior medial damage to the frontal lobes were not significantly affected in TMT Part B performance.

Adult↗
PubMed2000

Executive functions and the frontal lobes: a conceptual view.

Several problems in understanding executive functions and their relationships to the frontal lobes are discussed. Data are then presented from several of our studies to support the following statements: (1) the examination of patients with focal frontal lobe lesions is a necessary first step in defining the relation of executive functions to the frontal lobes; (2) there is no unitary executive function. Rather, distinct processes related to the frontal lobes can be differentiated which converge on a general concept of control functions; (3) a simple control-automatic distinction is inadequate to explain the complexity of control-automatic processes; (4) the distinction between complex and simple tasks cannot explain the differences in functions between the frontal lobes and other brain regions; and (5) the most important role of the frontal lobes may be for affective responsiveness, social and personality development, and self-awareness and unconsciousness.

Attention↗
PubMed2000

Acquisition of novel semantic information in amnesia: effects of lesion location.

Two patients with severe global amnesia are described who differ in the extent to which they have acquired new semantic information. Patient SS, who has extensive medial temporal lobe damage including the hippocampus as well as surrounding cortical areas, has failed to acquire virtually any new information regarding vocabulary or famous faces that entered the public domain since the onset of his amnesia. In contrast, patient PS, who has a selective lesion of the hippocampus proper, has gained a sense of familiarity of novel vocabulary and famous people, even though her effortful retrieval of this new semantic knowledge remains impaired. These findings extend to amnesia of adult onset, the proposal of Vargha-Khadem and colleagues that in patients with selective hippocampal injury, cortical areas surrounding the hippocampus may play an important role in new semantic learning [Vargha-Khadem, F., Gadian, D.G., Watkins, K. E., Connelly, A., Van Paesschen, W. and Mishkin, M., regarding the importance of the subhippocampal cortices in the mediation of new semantic learning in children with hippocampal lesions, Science, 1997, 277, 376-380].

Amnesia↗
PubMed2000

Wisconsin Card Sorting Test performance in patients with focal frontal and posterior brain damage: effects of lesion location and test structure on separable cognitive processes.

Forty-six patients with single focal lesions (35 frontal, 11 nonfrontal) were administered the Wisconsin Card Sorting Test (WCST) under three conditions of test administration. The three conditions varied in the amount of external support provided via specificity of instructions. The WCST, while a multifactorial test, is specifically sensitive to the effects of frontal lobe damage if deficits in language comprehension and visual-spatial search are controlled. There is also specificity of functioning within the frontal lobes: patients with inferior medial frontal lesions, unilateral or bilateral, were not impaired on the standard measures although they had increased loss of set when informed of the sorting categories. Verbal instructions may provide a probe to improve diagnosis and prognosis, assessment of the potential efficacy of treatment, and the time frame of plasticity of specific cognitive operations.

Brain Injuries↗
PubMed2000

Semantic capacities of the right hemisphere as seen in two cases of pure word blindness.

Two patients with pure alexia were studied with tachistoscopically presented stimuli to examine factors influencing their ability to distinguish words from nonwords and to derive semantic information at exposures too brief for explicit letter identification. Both patients had profound right hemianopia and computerized tomography (CT) evidence of splenial destruction. Both patients were successful in making word/nonword decisions for high-frequency, but not low-frequency, words. They could judge semantic class membership reliably for such common categories as animals and vegetables, but not for arbitrarily selected categories, such as office-related items. Judgments about the gender of people's names and place versus person name distinctions were made with high reliability. Results are interpreted as evidence for limited word recognition and semantic-processing capacity in the right hemisphere.

Aged↗
PubMed2000

Disorders of frontal lobe functioning.

The neurology of frontal lobe disorders can be summarized in descriptions of behavioral problems (apathy, etc.), of cognitive impairments (poor planning, etc.), and of motor deficits (grasp reflex, etc.). Reviews of this sort do not indicate, however, any regional specificity to the deficit profiles or identify any of the component processes of the complex deficits-what exactly is "poor planning"? In this review we present specific steps that assist in overcoming the limitations: (1) identify weaknesses in current understanding, (2) operationally define the processes to be analyzed, (3) review some methodologies that allow parsing of discreet processes into specific frontal regions, (4) review the unique advantages and disadvantages of the various neurological disorders that provide us with subjects for study, and (5) propose approaches to advance further a useful clinical neurology of frontal lobe disorders as well as a more finely grained scientific description of core frontal processes.

Aphasia↗
PubMed2000

Recovery rates after stroke and their impact on outcome prediction.

Current assessments do not provide reliable factors predictive of outcome from stroke for stroke survivors of intermediate age and severity of deficit. We sought to investigate whether early rate of functional improvement can facilitate prediction of functional outcome, length of stay, and disposition beyond that afforded by age and initial severity of deficit. Prospective study of consecutive admissions to acute rehabilitation (N = 244) with diagnosis of ischemic or hemorrhagic stroke. Independent measures were age, marital status, living situation, social situation, lag from symptom onset to rehabilitation, stroke type, admission score on the Functional Independence Measure (FIM), rate of FIM change (ROFC) as assessed by the best weekly FIM change in the first 3 weeks of rehabilitation. Dependent measures were functional status on discharge as assessed by a modification of Steinman's method, length of stay, and discharge disposition. Logistic regression analyses on each of the dependent measures identified significant factors, and interactions of significant factors were assessed by analysis of variance on continuous dependent variables. Cross-tabulations using significant factors from the logistic regression analyses were performed to identify groups with homogeneous outcomes. Groups with >80% homogeneity were considered likely to have predictive value. Discharge functional status: Admission FIM (AFIM) again fractionated the population into groups with poor outcome (AFIM <50 remained dependent), good outcome (AFIM >70 achieved nondependence), and an intermediate group with unpredictable outcome. In this intermediate group, ROFC had significant effect only for a small number of patients (n = 9) with rapid improvement (ROFC >25) who achieved nondependence. LOS: AFIM >70 had less than average LOS, ROFC = 10-15 FIM/week had longer than average LOS. LOS was significantly prolonged in patients with poor outcomes. Disposition: AFIM >70 and age <60 were strongly associated with home discharge. Patients not living at home before admission were not discharged home. Married patients had a greater tendency to home discharge than did those not married. ROFC had no bearing on disposition. ROFC has an independent influence on outcome but was sufficiently powerful in our sample to identify reliably only a very small subset of patients with otherwise indeterminate prognosis. LOS seems inordinately prolonged in patients with poor outcomes. Both of these results can guide efficient rehabilitation management.

Aged↗