A refined method to relate morphological and functional aspects of aphasia

Using human brain lesions to infer function: a relic from a past era in the fMRI age?

Recent technological advances, such as functional imaging techniques, allow neuroscientists to measure and localize brain activity in healthy individuals. These techniques avoid many of the limitations of the traditional method for inferring brain function, which relies on examining patients with brain lesions. This has fueled the zeitgeist that the classical lesion method is an inferior and perhaps obsolescent technique. However, although the lesion method has important weaknesses, we argue that it complements the newer activation methods (and their weaknesses). Furthermore, recent developments can address many of the criticisms of the lesion method. Patients with brain lesions provide a unique window into brain function, and this approach will fill an important niche in future research.

An evaluation of assumptions underlying the single-patient-only position in neuropsychological research: a reply

This note challenges the position adopted by A. Caramazza and W. Badecker (1989, Brain and Cognition 10, 256-295) that, since the a priori classification of patients can only be theoretically arbitrary, the basic unit of analysis in cognitive neuropsychology must be the individual patient. We argue that even if there is no prior theory to justify patient classification, this does not preclude group studies; syndromes are what the world gives us--they constrain theory, permitting groups to be formed for research purposes. We also reexamine a particular example of group-based research that was extensively criticized by Caramazza and Badecker. We confront each of their criticisms, and, again, demonstrate the validity of group-based research.

Mental planning and anticipatory processes with acute and chronic frontal lobe lesions: a comparison of maze performance in routine and non-routine situations

A series of computerized mazes were masked during presentation allowing only partial view of their structure. Patients suffering from acute or chronic unilateral frontal (medial, lateral) or retrorolandic (temporal, parietal) lesions and non-brain-damaged controls were required to pass through the mazes repeatedly, until they solved them without reaching a dead end. Because the mazes could not be viewed in their entirety at any one time, the subjects were forced to mentally generate and apply a plan of the maze. The first ("non-routine" situation), the second and the last ("routine" situation) trials of the mazes were analysed separately. The prefrontal cortex is supposed to subserve important functions in the planning of behaviour in unfamiliar, non-routine situations. Shallice (Phil. Trans. R. Soc. Lond. B298, 199-209, 1982; From Neuropsychology to Mental Structure, Cambridge University Press, Cambridge, 1988) therefore postulated that the behaviour of patients with frontal lobe lesions should not be disturbed in routine situations, but rather these patients should exhibit difficulties in dealing with new and unfamiliar situations. In the present investigation, patients with acute and chronic frontomedial lesions exhibited deficits in generating mental plans. Patients with acute frontomedial lesions made a larger number of errors in their second trials and subsequently required more trials to reach task criterium. Patients with chronic frontomedial lesions showed more frequent rule-breaking behaviour in their second trials. The analysis of maze performance in the first trial and that trial in which task criterion was achieved, showed that frontal lobe patients were impaired in neither routine nor non-routine situations. The observed results suggest a modification concerning Shallice's assumptions. Patients with frontomedial lesions are not generally incapable of dealing with non-routine situations. But they seem to be slower than patients with retrorolandic lesions and controls in profiting from experiences made in an unfamiliar, non-routine situation represented by the first explorations of new maze problems. This deficit can possibly be explained by the observation that anticipatory processes or the formation of expectations about possibly correct decisions in non-routine situations were altered in acute and chronic frontomedial patients. When these patients reached a maze intersection for the first time and therefore had no information about the continuation of the correct path, they showed significantly different intuitive directional decisions when compared to controls.

Long-term effects of cerebellar pathology on cognitive functions

Twelve patients with circumscribed chronic neocerebellar lesions but without CT-evidence of forebrain damage (other than the effects of shunting) were investigated for deficits of cognitive functions. Two different mechanisms were considered as possible causes of cognitive impairment: (1) Damage to the dentato-thalamo-cortical projection leading to impairments of cortical functions, and (2) prolonged intracranial pressure resulting in diffuse forebrain damage and subcortical dementia. Patients with lesions in the left neocerebellum showed deficits in cognitive operations in three dimensional space, consistent with the right forebrain dominance for spatial functions. Prolonged intracranial pressure, on the other hand, resulted in a mild overall cognitive impairment.

Computed tomographic patterns of proven embolic brain infarctions

To define patterns of infarction on computed tomography that are characteristic of embolism, as opposed to hemodynamically or microangiopathically induced brain lesions, a consecutive series of 60 patients with acute brain embolism were studied. Strokes were embolic in origin; that is, hemodynamic and in situ thrombotic stroke mechanisms had been excluded. Embolically active, cardiac disease was proved in 42 and was clinically evident in 13 patients. Five patients had suffered a stroke due to catheter-related embolism. Computed tomography revealed pial artery territorial infarction in 55 patients (92%). In 5, the infarction had the size or location (or both) characteristic of lacunes, although shape and lack of multiplicity raised questions about this interpretation. No patient showed a low-flow type of infarction pattern. These findings strongly support the view that (1) except for in situ thrombosis, pial artery territorial infarctions are indicative of an embolic mechanism, and (2) that the mechanism underlying lacunes is hardly, if ever, embolic.

Measurement of regional cerebral blood flow and accentuation of the primary auditory cortex with single photon emission computed tomography

Conventional brain scanning uses polar tracers which do not penetrate the normal blood-brain barrier. Radiolabeled amines like 123-iodoamphetamine (IMP) cross the barrier to inhibit serotonin and norepinephrine in synaptosomes. Studies of cerebral perfusion and function seem to be successful with such labeling. We advance the hypothesis for an increased IMP uptake in the stimulated primary auditory cortex. The method of single photon emission computed tomography (SPECT) is described. We have also been able to demonstrate marking of the primary auditory cortex by an increased amphetamine input in 6 out of 15 cases during stimulation by white noise.

Semiquantitative analyses of dynamic single photon emission computed tomography (SPECT) of the primary auditory cortex

To date it has not been possible to work out a standard quantification for single photon emission computed tomography (SPECT). Only one mathematical model has received general recognition, but the theoretical preconditions for this model are not fulfilled by iodine-amphetamine kinetics. A practical solution is offered by semiquantitative analysis. We have developed three computer programs for this analysis for perfusion and cerebral function studies of the symmetrically arranged brain.

Left hemisphere contribution to motor programming of aphasic speech: a reaction time experiment in aphasic patients

Simple reaction time to lateralized visual dot stimuli was studied in 10 fluent and 10 nonfluent right-handed chronic aphasics with left hemisphere lesions. As well as the standard simple reaction time condition, the patients were given a concomitant verbal task, requiring overt articulation while reacting to the visual stimuli. Compared with the control condition, in both aphasic groups the verbal task produced an overall lengthening of latencies, with a significant slowing down of responses to the stimuli located in the right visual half-field. According to these results the verbal concurrent activity appears to involve the left hemisphere as in normal subjects, suggesting that the undamaged regions of the left hemisphere have a role to play in the motor programming of aphasic speech. As a collateral finding, the difference between latencies to stimuli ipsilateral and contralateral to the responding hand--a measure of interhemispheric transmission time--is greatly increased in patients with motor deficits. This is consistent with the view that, in simple visuo-motor reaction time, interhemispheric transfer takes place between anterior regions of the brain.

Bereitschaftspotential in patients with unilateral lesions of the supplementary motor area

In the present study, an attempt was made to examine the sensitivity of the Bereitschaftspotential (BP) preceding simple finger movement in revealing pathophysiological patterns of premovement cortical activity in patients with chronic unilateral lesions of the supplementary motor area (SMA). Usually, in healthy subjects, BP has a clear maximum in Cz with larger amplitudes than in Ccon (located over the motor cortex, contralateral to the performing hand). In the patients, amplitudes did not differ between Cz and Ccon. This effect of the lesion on BP topography, was found in movements of either side. However, intraindividual comparisons revealed that the reduction of the BP in Cz (relative to Ccon) was larger for movements contralateral to the SMA lesion than for those ipsilateral of it.

The design and application of a data- and methodbase system for the Aachen Aphasia Test

The basic components of a data- and methodbase system useful for both individual diagnosis and (group-study) research in neuropsychology are described. Such a system enables one to organize, access and evaluate large data-sets of behavioural, neuroradiological and neurological information. The most important component of the system, the data- and methodbase management system, is described in some detail. It operates on databases comprised of Aachen Aphasia Test examinations and standardized CT evaluations as well as on methodbases containing various sets of analysis routines for the psychometric evaluation of (individual) aphasia test results and the evaluation and (graphical) presentation of standardized (individual) CT lesions. Although exemplified for AAT scores the techniques and principles employed are applicable to data- and methodbase systems in general.

Event-related brain potentials (P300) and neuropsychological deficit in patients with focal brain lesions

Sixteen patients with chronic focal brain lesions were investigated with an acoustic P300 test and psychological tests of spatial abilities (Maze Tracing Speed Test, Form Board Test), cognitive speed (Sequential Number Connection Test), categorization (Figure Sorting Test), verbal fluency and vigilance. Neither the psychological battery nor P300 analysis discriminated frontal from retrorolandic brain lesions. Abnormalities of P300 significantly correlated with impairments in those psychological tests which had a spinal component in common. We suggest that abnormality of the P300 with focal brain damage rather indicates higher mental function impairment than direct effects of the lesion.

A microcomputer assisted method for obtaining composite pictures of focal brain damage

A method used to produce composite drawings of superimposed areas of brain infarction is described. The method uses a microcomputer interfaced to a digitising pad and linear plotter. Areas of brain damage are drawn on standardised maps, digitised, manipulated in computer memory, and summated using computer graphics facilities. The composites show the position of brain damage in groups of patients as a contour map of the extent of lesion overlap. The method can be used to study neurological and neuropsychological deficits using CT-scan, or other imaging techniques. Deep and superficial lesions may be displayed equally well.

Lesions of the basal ganglia, thalamus, and deep white matter: differential effects on language functions

Forty-five patients with unilateral demarcated vascular lesions in the basal ganglia, the thalamus and the deep white matter were investigated with an "aphasia battery." Patients with basal ganglia lesions performed worse than both other groups in tests of articulation, syntax, and lexical functions. The deficit of patients with basal ganglia lesions on all expressive language modalities was lateralized to the left hemisphere. Patients with left thalamic lesions showed impairments of speech fluency and in the Token Test. Patients with white matter lesions alone showed no effect of laterality in tests of language functions. The results are discussed on the basis of a recent theory of the participation of the deep nuclei in language processing.

CT scan correlates of gesture recognition

The ability to recognise gestures was studied in 65 left-hemispheric stroke patients whose lesions were located by CT scan. In the acute stage (first month) frontal lobe and basal ganglia were frequently involved in patients showing inability to recognise gestures. In the later (third to fourth month) and chronic stages (greater than 6 months) parietal lobe involvement was important; lesions causing gesture recognition impairment were larger, had more extensive and frequent parietal involvement and produced less temporal lobe damage than those causing aural comprehension defects. These findings are discussed in the light of recent models of cerebral localisation of complex functions.

Language and cognitive deficits resulting from medial and dorsolateral frontal lobe lesions

A total of 36 patients with chronic unilateral circumscribed medial and dorsolateral frontal lobe lesions were investigated with a range of neuropsychological tests. Lateralized deficits in tasks depending on language functions were found with dorsolateral but not with medial lesions. The specific role of Broca's area could not be confirmed. Lesions of the supplementary motor area led to mild deficits in tests of "concept formation". Frontomedial lesions situated more deeply in the interhemispheric fissure resulted in memory deficits. The results are discussed on the basis of recent neurophysiological theories of brain function.

Structure of human auditory cortex. III. Statistical analysis of dendritic trees

3-Dimensional coordinates of Golgi-impregnated neurons in left and right human areas TA, TB and TC were stored using computer microscopy. The tangential extent of neurons was taken to be an estimate of their effective radius, which is a compromise between their maximum radius and the average tangential projection of their dendrites. Analysis of variance and t-test comparisons were made among the areas and between the hemispheres on a total data base of 622 neurons. It was assumed that the neurons are organized in functional columns. The tangential extent of left-hemisphere columns is absolutely larger than on the right, but is smaller relative to the column-column interval. Neuropil on the left is packed more densely with dendrites belonging to the nearest column. It seems that during the course of evolution interconnected units (as in the right hemisphere) have become more disentangled (left hemisphere), yielding perhaps a greater capacity for differentiated responses in the latter case. A more detailed analysis revealed that much of the difference between areas and/or hemispheres was due to the pyramidal neurons. The structure of non-pyramidal cells is relatively consistent within each hemisphere and shows non-systematic differences between the hemispheres.