Different types of abstract concepts: evidence from two neurodegenerative patients.

The observation of neurological patients showing selective impairments for specific conceptual categories contributed in the development of semantic memory theories. Here, we studied two patients (P01, P02), affected, respectively, by the semantic variant of Primary Progressive Aphasia (sv-PPA) and Cortico-Basal Syndrome (CBS). An implicit lexical decision task, including concrete (animals, tools) and abstract (emotions, social, quantity) concepts, was administered to patients and healthy controls.P01 and P02 showed an abolished priming effect for social and quantity-related concepts, respectively. This double dissociation suggests a role of different brain areas in representing specific abstract categories, giving insights for current semantic memory theories.

Artistic productivity and creative thinking in Parkinson's disease.

BACKGROUND AND PURPOSE: Creative drive and enhanced artistic-like production may emerge in patients with Parkinson's disease (PD) during dopaminergic therapy. However, it has not been described to date whether this artistic-like production results from dopaminergic drugs triggering innate skills or it could be considered as a repeated behavior possibly associated with impulse control disorders (ICDs). METHODS: We investigated creative drive in a cohort of cognitively preserved patients with PD by means of the Torrance Test of Creative Thinking (TTCT). We also investigated a putative association between creative drive and ICDs in 36 PD patients with (PD-c) or without (PD-nc) increased artistic-like production and 36 healthy controls (HC). We considered artistic-like productivity to be enhanced if patients reported working on any form of art more than 2h per day after the introduction of dopaminergic treatment. The TTCT, the Barratt Impulsiveness Scale (BIS-11A), the Minnesota Impulsive Disorders Interview (MIDI), and the Punding Rating Scale were applied. RESULTS: Mean TTCT score of PD-c was found to be similar to HC (169.4±51.6 vs. 170.2±69.7, respectively), and both PD-c and HC had significantly higher TTCT scores than patients with PD-nc (125.4±46.1 P<0.05). TTCT did not correlate with any demographic or clinical data in both PD subgroups. No correlation was found between TTCT, BIS-11A, and MIDI. CONCLUSIONS: Our study suggests that newly acquired artistic-like production in patients with PD is not associated with impulsivity or ICDs. Artistic-like production might represent the emerging of innate skills in a subset of predisposed patients with PD on dopaminergic therapy.

Unilateral neglect and space constancy during passive locomotion.

Space constancy was investigated in seven blindfolded left-neglect patients by driving them along routes involving one or two, left or right, 90 degrees turns. At the end of each route patients had to indicate its starting point while still blindfolded. On average, no considerable left/right differences were found in pointing accuracy. The entailments of this finding for the understanding of neglect phenomena are briefly discussed.

Semantic amnesia without dementia: documentation of a case.

We described the case of a patient affected by a progressive semantic memory disorder associated with prevalent temporal lobe atrophy. This deficit seems to be "pure" in the sense that it has not been found to overlap with other cognitive deficits (intellectual, linguistic, perceptual, visuo-spatial etc.) for a long time. Furthermore, despite his impaired semantic knowledge, the autobiographical memory of the patient was largely intact. This case therefore represents a form of "semantic amnesia" without dementia, and supports the hypothesis that there is a partial distinction between "semantic" and "episodic" memory.

Modulation of neglect hemianesthesia by transcutaneous electrical stimulation.

The effects of transcutaneous electrical stimulation on deficits of tactile perception contralateral to a hemispheric lesion were investigated in 10 right brain-damaged patients and in four left brain-damaged patients. The somatosensory deficit recovered, transiently and in part, after stimulation of the side of the neck contralateral to the side of the lesion, in all 10 patients with lesions in the right hemisphere, both with (six cases) and without (four cases) left visuo-spatial hemineglect, and in one left brain-damaged patient with right hemineglect. In three left brain-damaged patients without hemineglect, the treatment had no detectable effects. In one right brain-damaged patient, the stimulation of the side of the neck ipsilateral to the side of the lesion temporarily worsened the somatosensory deficit. These effects of transcutaneous electrical stimulation are similar to those of vestibular stimulation. The suggestion is made that these treatments modulate, through afferent sensory pathways, higher-order spatial representations of the body, which are pathologically distorted toward the side of the lesion. The modulatory effect is direction-specific: the defective internal representation of the contralesional side may be either partly restored, improving the disorder of tactile perception, or further impoverished, worsening the deficit. The possible neural basis of this modulation is discussed.

Analogical representation and language structure.

Severe impairment of the analogue of mental representation is not compensated for by putative language-based cognitive processes in non-dysphasic brain-damaged patients. This undermines the hypothesis of an independent role for language in the generation of thought. Against this view it may be contended that there seems to be no obvious way in which analogical mental representation can decide between alternative syntactical structures available for the expression of thought. We performed a visual imagery experiment in which we asked 40 subjects to imagine visual scenes representing the meanings of simple utterances presented to them. The subjects then had to indicate the relative position, in each visual image, of two objects mentioned in each utterance. Series of utterances were presented differing syntactically (active or passive phrase) and semantically (specifying in different ways the spatial and temporal relations between the objects mentioned). The results of this mental imagery experiment indirectly support the hypothesis that syntactical structures can be represented in a nonlinguistic analogue medium.

Vestibular stimulation, spatial hemineglect and dysphasia, selective effects.

The selectivity of the effects of vestibular stimulation was investigated in a left brain-damaged patient suffering from right visuo-spatial hemineglect and severe dysplasia. Vestibular stimulation temporarily improved the former but not the latter disorder. These results support the view that this treatment improves hemineglect by a specific effect, running counter the rightward distortion of egocentric co-ordinates, rather than by a general hemispheric activation.

Dissociation of ophthalmokinetic and melokinetic attention in unilateral neglect.

A line cancellation task was performed by 36 right brain-damaged patients with unilateral neglect under four different conditions: normal and mirror-reversed view, with and without cueing. Two types of unilateral neglect were distinguished by directing ophthalmo- and melokinetic components of visuomanual scanning to opposite sides of the stimulus array. In ophthalmokinetic neglect, contralesional visual scanning of the stimulus array was defective, while manual scanning was unimpaired. The converse was true of melokinetic neglect. Ophthalmokinetic neglect was predominantly associated with posterior brain damage, while melokinetic neglect was predominantly associated with frontal or subcortical brain damage. In a few instances, cueing visuomanual scanning toward the neglected side of the stimulus array converted ophthalmokinetic into melokinetic neglect, and vice versa. The results are held to be indicative of two components of space representation and to provide further evidence of response-driven modulation of perceptual awareness.

Improvement of left visuo-spatial hemineglect by left-sided transcutaneous electrical stimulation.

The effects of transcutaneous electrical stimulation on left visuo-spatial hemineglect, assessed by a visuo-motor exploratory task (letter cancellation), were investigated in patients with right hemisphere lesions. In Experiment 1 left neck stimulation temporarily improved the deficit in 13 out of 14 patients (93%), while stimulation of the right neck had no positive effects, worsening exploratory performance in nine patients (64%). Experiment 2 showed that left neck stimulation temporarily improved neglect also when head movements were prevented by a chin-rest. In Experiment 3, stimulation of both the left hand and left neck had comparable positive effects on visuo-spatial hemineglect. These results are interpreted in terms of: (1) non-specific activation of the right hemisphere, contralateral to the stimulation side; (2) specific directional effects of left somatosensory stimulation on the egocentric co-ordinates of extra-personal space, which in neglect patients are distorted towards the side of the brain lesion.

Challenging current accounts of unilateral neglect.

Two left-neglect patients were asked (i) to bisect a 15 cm line, (ii) to bisect the empty space between the endpoints of a 15 cm virtual line, and (iii) to set the endpoints of a 15 cm virtual line, given its midpoint. With one patient, the subjective midpoint of the virtual line was found to be displaced leftwards with respect to the subjective midpoint of the real line, whereas with the other it was found to be displaced rightwards. However, in condition (iii) both patients significantly underestimated the distance from the centre of the rightmost point of the virtual line while relatively overestimating that from the centre to the left endpoint. This latter result challenges current accounts of unilateral neglect.

Anatomical correlates of visual and tactile extinction in humans: a clinical CT scan study.

The anatomical correlates of tactile and visual extinction with double simultaneous stimulation were investigated in a series of 159 patients with right brain damage caused by stroke. Forty six patients showed extinction (22 tactile, 14 visual, 10 tactile and visual). Over 50% of the patients with extinction had deep lesions, which were found in about 25% of the patients with visuospatial neglect not associated with extinction. In the patients with extinction and cortico-subcortical damage the paraventricular occipital white matter and the dorsolateral frontal cortex were most often involved. By contrast, when neglect was also present, the lesions clustered in the inferior parietal lobule. These data suggest, from an anatomical perspective, that partly different neural mechanisms may underlie neglect and extinction. The comparatively high frequency of subcortical lesions involving the ascending pathways may be a neural correlate of a sensory component of extinction.

Unilateral neglect in route description.

Route description was investigated in two patients suffering from left unilateral neglect. Both had evident difficulty with left turns. This finding suggests that the topological correspondence between represented environment and representational mechanisms in the brain is not confined to frozen (picture-like) perspectives.

Exploring somatosensory hemineglect by vestibular stimulation.

The effects of vestibular stimulation upon somatosensory deficits or tactile extinction contralateral to a hemispheric lesion were investigated in 20 right brain-damaged patients and 11 left brain-damaged patients. After stimulation, right brain-damaged patients showed a temporary partial recovery from left hemianaesthesia or extinction. Conversely, right somatosensory deficits associated with left brain damage were virtually unaffected by vestibular stimulation. Temporary recovery from somatosensory deficits was independent of the presence of visuo-spatial hemineglect. The suggestion is made that somatosensory deficits and extinction produced by right brain damage have an important non-sensory or perceptual component, that may be positively affected by vestibular stimulation. The mechanisms whereby this treatment may ameliorate somatosensory deficits may involve the restoration of the normal correspondence between somatotopic and egocentric representations of the body.

Hemianopia, hemianesthesia, and spatial neglect: a study with evoked potentials.

We recorded somatosensory or visual evoked potentials (SEPs, VEPs) to stimuli contralateral and ipsilateral to the lesion in three right-brain-damaged patients with left spatial hemineglect and in three left-brain-damaged patients without evidence of neglect, as assessed by visual exploratory tasks. All patients had contralateral homonymous hemianopia or hemianesthesia. The three neglect patients showed normal SEPs or VEPs to stimuli delivered to the left half-field or to the left hand, without conscious perception and verbal report of the stimulation. By contrast, the three left-brain-damaged patients without neglect showed no recognizable cortical evoked response to contralateral visual or somatosensory stimuli. In all patients, the cortical evoked responses to ipsilateral stimulation were normal. In patients with spatial hemineglect, hemianopia and hemianesthesia may be manifestations of the neglect syndrome (visual and somatosensory hemi-inattention), rather than representing primary sensory deficit. Visual and somatosensory hemi-inattention may be due to defective access to the neural processes subserving conscious perception by information that has undergone early sensory processing.

Visual and nonvisual neglect after unilateral brain lesions: modulation by visual input.

A spatial exploratory task was given to 110 patients with unilateral brain lesions [66 right brain-damaged (RBD) patients and 44 left brain-damaged (LBD) patients] in two conditions, with and without the aid of vision. Exploratory deficits mainly involved the contralesional half-space and were most frequently associated with right brain damage. A double dissociation was found between the visual and the nonvisual conditions of the task; selective impairments in the visual and in the nonvisual condition were associated with the presence and the absence of visual field deficits, respectively. The suggestion is made that discrete "visual" and "tactile-kinesthetic" spatial representational systems are involved in exploration of extrapersonal space. A further distinction is made between input and output spatial system. The association between visual field deficits and visual neglect is explained in terms of the impairment of an input visuospatial component, which feeds an output component involved in spatial exploration. Finally, the ambiguous nature of the visual field deficits in neglect patients is discussed and the suggestion is made that an attentional modality-specific nonsensory component may be present.

Hemianesthesia, sensory neglect, and defective access to conscious experience.

We report a patient with an ischemic stroke in the vascular territory of the right middle cerebral artery who had left spatial neglect and left hemianesthesia. The patient showed a dissociation between defective verbal reporting of somatosensory stimuli delivered to the left hand and physiologic evidence from an autonomic index. This indicates that there was processing of undetected stimuli without the patient's awareness, and suggests that the hemianesthesia was due, at least in part, to somesthetic hemi-inattention.

Remission of somatoparaphrenic delusion through vestibular stimulation.

The effects of vestibular stimulation on somatoparaphrenic delusion were investigated in a patient suffering from a fronto-temporo-parietal infarction located in the right hemisphere. Transitory remission of the patient's delusional belief was consistently observed during unilateral vestibular activation obtained by means of cold-water irrigation of the left (contralesional) ear.

Break-down of perceptual awareness in unilateral neglect.

Four neglect patients are reported who where unable to detect left-side differences in pairs of drawings though being sometimes influenced by such differences in making preference judgements. In most instances, tracing the silhouette of the drawings did not help patients to find the difference despite the fact that tracing implied crossing the altered detail or following its contour with the fingertip. This finding cannot easily be accommodated by current theories of unilateral neglect.

Perceptual and premotor factors of unilateral neglect.

Right-brain-damaged patients showing unilateral neglect underwent a specifically devised line-bisection task that allowed uncoupling of the direction of visual attention from that of hand movement. This made it possible to isolate and separately assess perceptual and premotor factors of the disorder. Comparison of experimental and radiologic data suggested that premotor factors were more pronounced in patients with lesions involving the frontal lobes than in patients with lesions confined to postrolandic areas. The technique employed is compatible with bedside examination and provides data useful for standard assessment of neglect symptomatology for both clinical and experimental purposes.

Temporary remission of left hemianesthesia after vestibular stimulation. A sensory neglect phenomenon.

In three right-brain damaged patients with contralesional neglect vestibular stimulation induced a temporary remission of left hemianesthesia, in addition to the well-known transient recovery of extrapersonal and personal neglect. These findings indicate that in neglect patients attentional factors may play an important role in producing apparently "primary" sensory deficits, which may be interpreted in terms of defective access to conscious processing.