E. De Renzi

Are Semantic Systems Separately Represented in the Brain? The Case of Living Category Impairment

Following herpes encephalitis, a patient showed impaired knowledge of animals, fruits and vegetables, flowers and food (so called living things categories), whatever the modality in which stimuli were presented and responses were given. A series of experiments showed that the deficit specifically affected the ability to retrieve the perceptual features of the living stimuli defining their shape, while knowledge of their functional-encyclopedic properties was preserved. The patient had no problems with man-made objects, except when the recall of their colour, or the identification of their sound was requested. It is argued that the retrieval of the perceptual features was potentially disrupted for every type of category, but that the block was compensated for man-made objects, because the close correspondence between shape and function that characterises them provided an alternative route to access their structured form representations. On this account, the selective deficit for living categories seems contingent on the interaction between an overall cognitive impairment--the deficit in retrieving perceptual features--and some intrinsic properties of the stimulus--the factors that have modelled its form--and cannot be taken as evidence that semantic systems are allotted to separate cerebral areas.

Oral Apraxia and Aphasia

Summary This study was undertaken in order to assess the frequency and to explore the role of oral apraxia in expressive disturbances of speech. Forty right brain damaged patients, 134 left brain damaged patients and 40 control patients were given an oral apraxia test and a limb apraxia test for intransitive movements. In the left hemispheric group the presence and quality of aphasia was assessed by means of a standard aphasia examination. On the oral apraxia test, the performance of the right hemispheric group was similar to that of the control group. All the left brain damaged patients who scored below the lowest score obtained by any of the right brain damaged patients were considered oral apraxic. A strong association was found between oral apraxia and phonemic-articulatory disorders of speech, the exceptions being mainly in the sense of a poorer verbal than praxic performance. However, severe oral apraxia was found in two non aphasic left brain damaged patients. When considered with respect to the clinical syndromes of aphasia, it was found that oral apraxia was a very common accompaniment of Brocas aphasia and of phonemic jargon aphasia, it was present in one third of conduction aphasics and it was usually absent in Wernickes aphasia. Oral apraxia was not uncommonly found to be independent of limb apraxia. Moreover, the majority of patients with severe oral apraxia and mild or no phonemicarticulatory disturbances did not show limb apraxia: therefore, one cannot argue that, in these cases, oral apraxia was part of a general praxic disturbance.

Spatial Memory and Hemispheric Locus of Lesion

Corsis cube test was given to 40 control and 80 brain-damaged patients to assess the relation of different aspects of spatial memory to the hemispheric locus of lesion. Spatial span was found affected by injury producing visual field defect (VFD), regardless of the side of the lesion. Delayed reproduction of a 3 cube sequence (which was within the span of every patient) was performed more poorly by patients with right hemisphere damage and VFD than by controls. This was true whether the delay was unfilled or filled with a counting activity, the two conditions being equally effective in bringing about the inferiority of the right brain-damaged group. Learning to criterion up to a maximum of 50 trails a supraspan sequence was failed by 65% of right brain-damaged patients with VFD, a percentage significantly higher than that found not only in the control group, but also in any other brain-damaged group. These findings point to the dominant role played by the posterior region of the right hemisphere in subserving spatial memory mechanisms, especially when the acquisition of stable traces is requested.

Bilateral paramedian thalamic artery infarcts: report of eight cases.

Eight consecutive patients with CT scan evidence of a bilateral infarct in the territory of the paramedian thalamic artery are reported. In seven cases the infarct also extended to the territory of the polar artery. The main symptoms were: disorder of vigilance which cleared in a few days, and hypersomnolence which lasted longer and in two patients was still present a year later; amnesia, detectable clinically in four patients and only with tests in two patients, which persisted in one patient for three years; changes of mood and bulimia present in five and four patients respectively; and vertical gaze paresis in five patients. Only one patient died, and in the remainder the symptoms tended to subside, but none of the patients who could be followed-up for a year returned to normal behaviour. Clinical and CT scan correlations pointed to the mammillo-thalamic tract as the structure whose damage was responsible for the memory disorders.

Hemispheric Contribution to Exploration of Space Through the Visual and Tactile Modality

Summary Control and unilaterally brain-damaged patients were given two tests requiring the exploration of space through the visual and the tactile modalities. In the visual test, the patient was required to identify a number on a display board among alternatives, while in the tactile test he had to find a marble in a maze. The score was the time spent in searching for the item. On the visual test, controls performed better when the item was on the left side than when it was on the right. This “normal” left-right gradient (probably due to reading habits) was found to be significantly increased in left brain-damaged patients and reversed in right brain-damaged patients, a finding which supports the assumption that injury to one hemisphere mainly impairs the exploration of contralateral field. On the tactile test, each hemispheric group performed worse in the contralateral field. This lengthening of the searching time cannot be explained by disruption of the sensorimotor mechanism subserving space exploration and points to the impairment of a higher level ability, identifiable as the representation of contralateral space. When performance was scored in terms of failure in finding the marble within the 90 sec time limit, right hemisphere patients with visual field defects turned out to be significantly more impaired than any other brain-damaged subgroup. This finding is suggestive for the occurrence of unilateral neglect also in the tactile modality and it lends support to the hypothesis that hemi-inattention does not depend so much on perceptual and motor factors as on a mutilated representation of space.

Attentional Shift Towards the Rightmost Stimuli in Patients with Left Visual Neglect

In a search task where four letters were displayed to the right of a central fixation point, right brain-damaged patients with visual neglect showed the fastest response when the target was at the rightmost position and progressively slower responses as it moved towards the center of the display. This finding confirms Kinsbournes claim that in visual neglect an important role is played by the magnetic attraction that the extreme end of the right structured space exerts on the patients attention.

The Influence of Aphasia and of the Hemispheric Side of the Cerebral Lesion on Abstract Thinking

Summary A modified version of Weigl Sorting Test which allows 5 criteria of classification was administered to 40 control patients, 40 right brain-damaged patients, 22 left non-aphasic brain-damaged patients and 45 aphasics. The performance of the 4 experimental groups was analyzed by means of co-variance analysis, independent variables being age, years of schooling and RT. Right and left non-aphasic brain-damaged patients performed not differently from control patients on Weigl test, while the mean score of the aphasic group turned out to be about one half of that of the control group. The analysis yielded the same results also when the score obtained by the patients on a general intelligence test (Ravens P. M. 1938) was introduced as an additional independent variable. The score obtained by aphasics on Weigl test was found to correlate highly with an auditory verbal comprehension score, while no significant correlation was found between Weigl score and either a visual naming or an ideomotor apraxia score. Patients with typical “amnesic” aphasia were not found to perform the test more poorly than patients with typical Wernickes or Brocas aphasia. In conclusion, these data indicate that Weigl test is not sensitive to the presence of cerebral damage per se while it is highly sensitive to the presence of left (dominant) hemisphere lesions associated with aphasia. The evidence pointing to a specific defect of “abstract thinking” in aphasics may be interpreted as the consequence of a disruption of “inner language” in these patients; however, an alternative view may be advanced, viz., that the same areas subserving linguistic activities in the left hemisphere are also specialized in carrying out intellectual tasks of a symbolic nature.

Imitation and utilisation behaviour.

OBJECTIVE: To investigate the incidence, anatomical correlates, and clinical features of imitation and utilisation behaviour, which are thought by Lhermitte and coworkers to represent a reliable and frequent index of frontal lobe disease. METHODS: 78 patients with hemispheric local lesions were tested in two separate sessions, in which their reactions to a series of gestures performed by the examiner and to the presentation of a set of objects were recorded. The patients were stratified into a frontal (n = 52) and a non-frontal group (n = 26) on the basis of their CT data. RESULTS AND CONCLUSIONS: Imitation behaviour was present in 39% of the frontal patients and was mainly associated with medial and lateral lesions, at odds with the claim of Lhermitte et al that it is a constant accompaniment of lower, mediobasal lesions. In the non-frontal group it was found in three patients, all with damage to the deep nuclei region. Utilisation behaviour was a much rarer phenomenon, present in only two patients, both of whom had frontal damage. Neither imitation behaviour nor utilisation behaviour were found in patients with retrorolandic cortical lesions.

An experimental investigation on the nature of extinction

Under conditions of bilateral simultaneous presentation a right brain-damaged patient consistently extinguished visual stimuli presented for 200 msec to the left visual field. He was submitted to a series of experiments aimed at assessing the variables that influence this phenomenon. Extinction persisted unmodified when stimulus presentation was lengthened to 500 msec, when the size of the left stimulus was four-fold that of the right stimulus and for whatever position the stimuli occupied on the two halves of the display. Single stimuli were always perceived, but their localization was transposed rightward. The only condition in which extinction was partially reduced was when the instructions called for total disregard of the right stimulus. The patient also extinguished the leftmost of two stimuli presented in the left space, while he always perceived both stimuli when they were presented in the right space. However, if attention was covertly moved to a point in the right space and two stimuli were displayed to either side of it, left stimuli were neglected 70% of the time. Though a left stimulus was never perceived, it slowed the RT to the identification of a right stimulus. These data are interpreted in the frame of the directional bias theory, which attributes extinction to a shift of attention towards the side ipsilateral to the lesion, caused by the imbalance between the opponent turning processors, controlled by the right and left hemisphere. However, the striking difference in the rate of extinction when both stimuli were presented to the left or to the right field implies a stepwise decrement in the deployment of attention by the damaged processor, when it enters in the opposite space.

Dense Retrograde Amnesia, Intact Learning Capability and Abnormal Forgetting Rate: A Consolidation Deficit?

Following a thoracic trauma, which caused brain hypoxia, a 24-year-old man presented with a dense retrograde amnesia for events, persons and environments that spanned his whole life before injury. Knowledge acquired at school or through the media were equally lost, with the exception of arithmetical skills and some geographical knowledge. No deficit was apparent in language, object recognition, motor skills and intellectual tests. Anterograde memory was marked by very efficient learning capacity, an almost perfect retention of information at delay interval of 4 hours and pathologically rapid forgetting at longer delays. Informal observations agreed with test performance in showing that he could relearn facts of the past and easily acquire new information, but tended to lose these memories if the information was not frequently rehearsed. PET showed a hypometabolism of the posterior temporal lobes. Though some points remain obscure, we propose that a consolidation deficit hypothesis provides the most sensible interpretation of this peculiar pattern of memory deficit.