Bi-hemispheric transcranial direct current stimulation for upper-limb hemiparesis in acute stroke: a randomized, double-blind, sham-controlled trial

BACKGROUND AND PURPOSE

Neuromodulation is a promising approach to increasing motor recovery in stroke; however, to date, there is a scarcity of evidence documenting the clinical potential of transcranial direct current stimulation (tDCS) administered in the acute phase of stroke. The present study aims to examine the clinical effects of a treatment involving the application of tDCS in the acute stage post-stroke.

METHODS

This was a randomized, double-blind, sham-controlled trial. A cohort of 32 stroke patients with severe motor impairment underwent 5 days of treatment with real or sham bi-hemispheric tDCS over the motor cortex. During the treatment, tDCS was applied twice per day (two daily applications each of 15 min), starting 48 to 72 h after stroke onset.

RESULTS

We found statistically significant improvements after both real and sham tDCS treatments in primary (hand grip strength, Motricity Index) and secondary (National Institutes of Health Stroke Scale score, Barthel Index) outcomes. Patients receiving real tDCS showed a larger improvement of upper-limb muscle strength at the end of treatment phase; this advantage was no longer present after 6 months.

CONCLUSIONS

Transcranial direct current stimulation may be used to accelerate the rate of upper-limb motor recovery during the spontaneous recovery period.

Phonological Short-term Memory and the Learning of Novel Words: The Effect of Phonological Similarity and Item Length

The investigation of a patient with a selective impairment of phonological short-term memory has recently provided evidence that this system may be involved in long-term learning of novel words, for which a pre-existing semantic representation is not available (Baddeley, Papagno, & Vallar, 1988). The present series of experiments in normal subjects explored this hypothesis. We assessed the effects of phonological similarity and item length, which reflect the operation of the phonological short-term store and the rehearsal component of verbal memory, upon paired associate long-term learning of auditorily presented words and non-words. Phonological similarity affected the learning of novel words more than known words (Experiment 1); when a delay was interposed between presentation and recall, the disruptive effect was confined to novel words (Experiment 2). Also word length disrupted the learning of novel words, but not of known words (Experiment 3). These results tie in with neuropsychological evidence to suggest a role for phonological short-term memory in the learning of new words, and they have developmental implications for the study of language acquisition.

Facial macrosomatognosia and pain in a case of Wallenberg's syndrome: selective effects of vestibular and transcutaneous stimulations

Macro- and micro-somatognosia refer to rare disorders of the cerebral representation of the body whereby patients perceive body parts as disproportionately large or small. Here we report the experimental study of a patient who, following a left lateral medullary stroke (Wallenberg's syndrome, including vestibular deficits) complained of a persistent somatosensory illusory sensation of swelling, confined to the left side of his face (i.e., left macrosomatognosia). This hemifacial somatosensory distortion was associated with a left facial anesthesia, and a neuropathic pain affecting the three branches of the left trigeminal nerve. In this study, we first document quantitatively the patient's somatosensory illusion by using a somatosensory-to-visual matching task in which the patient modified the picture of his own face to fit his left-sided somatosensory misperception. The patient's performance revealed that macrosomatognosia was confined to the second branch of the left trigeminal nerve. Perception of the size of visual objects was comparatively preserved. Second, we investigated the effects of two peripheral stimulations, which may affect the spatial component of somatosensory deficits (caloric vestibular stimulation, CVS; transcutaneous electrical nervous stimulation, TENS) and pain (TENS). Left CVS abolished the facial somatosensory illusion, for about 30min, but had no effect on the left facial pain. Conversely, left TENS substantially reduced the neuropathic pain during stimulation, but had no effect on macrosomatognosia, indicating a double dissociation between the two disorders. These results reveal that facial macrosomatognosia may be regarded as a high-order deficit of somatosensory perception of the shape and volume of the face, which fits the definition of 'hyperschematia' (i.e., when the body takes up too much room) originally proposed by Bonnier (1905). Our data also indicate that CVS may favor the restoration of the conscious representation of the shape and size of the face. Overall, these findings lend support to the view that afferent inputs from the vestibular system can affect in a specific fashion the activity of cerebral structures involved in the building up and updating of the topological description of body parts.

Supercalifragilisticexpialidocious: how the brain learns words never heard before

Vocabulary acquisition is such a major aspect of language learning in children, but also in adults when learning a foreign language, that a dedicated vocabulary learning device may exist within the language organ. To identify the relevant brain systems, we performed regional cerebral blood flow measurements in normal subjects while they were learning a list of neologisms or a list of word-nonword pairs. Structures implicated in phonological short-term memory (Broca's area, left temporo-parietal junction) were steadily activated during nonwords learning, while the left temporal lobe neocortical and paralimbic structures (parahippocampal region), associated with long-term memory, contributed to learning in a time-dependent manner, with maximal activation at the beginning of the process. The neural system specifically activated when learning new vocabulary was strongly lateralized to the left hemisphere. This evidence refines current models of memory function and supports theories which emphasise the importance of phonological competence in hemispheric dominance for language.

Left size distortion (hyperschematia) after right brain damage

OBJECTIVE

To quantitate a size distortion involving the side of space contralateral to the lesion (contralesional) in two right-brain-damaged patients.

METHODS

We studied two right-brain-damaged patients with lesions sparing the occipital lobe and a mild left neglect on target cancellation or line bisection. The lesions involved the temporoparietal region (Patient 1) and the basal ganglia and the insula (Patients 1 and 2). Patients were given drawing tasks and tasks requiring perceptual and visuomotor judgments of horizontal extent.

RESULTS

In drawing objects such as a daisy both from memory and by copying, patients exhibited a disproportionate enlargement of the left-hand side of objects and added more left-sided petals to the drawn daisy. This pathologic behavior persisted when the patients were blindfolded and was likely to reflect a perceptual, rather than premotor, size distortion. In a task requiring the perceptual matching of two rectangles, patients underestimated the left-sided stimulus. In a visuomotor task requiring the reproduction of the horizontal extent of a segment, patients exhibited a hyperextension, when a leftward movement was required.

CONCLUSIONS

We showed a disordered representation of extrapersonal space, possibly involving a contralesional relaxation of the spatial medium. The deficit does not arise at the level of retinotopic coordinate frames and is independent of unilateral spatial neglect.

Left caloric vestibular stimulation ameliorates right hemianesthesia

BACKGROUND

Left caloric vestibular stimulation (CVS) transiently reduces impairments of right-brain-damaged patients with left unilateral neglect, including left hemianesthesia, contralateral to the side of the lesion (contralesional). Conversely, no effect on right contralesional hemianesthesia in left-brain-damaged patients is seen with right CVS. This discrepancy is unexplained.

METHODS

The authors explored the effect of CVS on right- and left-brain-damaged patients with hemianesthesia. One left-brain-damaged patient had an fMRI study during tactile stimulation before and after left CVS. The same fMRI touch study, without CVS, was performed in neurologically unimpaired subjects.

RESULTS

A transient remission of right hemianesthesia associated with left brain damage was observed, provided that cold CVS was administered to the left ear. In the left-brain-damaged patient studied with fMRI, left CVS modulated the neural response to right hand tactile stimuli of a portion of the secondary somatosensory area (SII) of the right hemisphere. In neurologically unimpaired subjects, fMRI scans showed that the same part of area SII in the right hemisphere was activated by ipsilateral right-sided touches and to a larger extent than area SII in the left hemisphere by left-sided touches.

CONCLUSIONS

Left caloric vestibular stimulation is effective on both left and right hemianesthesia because it modulates the hemisphere that has a more complete representation of, or is capable to attend to, the whole somatosensory surface of the body. These results suggest a hardwired hemispheric asymmetry in hand representation, starting from a somatotopically organized brain region such as area SII.

Shared cortical anatomy for motor awareness and motor control

In everyday life, the successful monitoring of behavior requires continuous updating of the effectiveness of motor acts; one crucial step is becoming aware of the movements one is performing. We studied the anatomical distribution of lesions in right-brain-damaged hemiplegic patients, who obstinately denied their motor impairment, claiming that they could move their paralyzed limbs. Denial was associated with lesions in areas related to the programming of motor acts, particularly Brodmann's premotor areas 6 and 44, motor area 4, and the somatosensory cortex. This association suggests that monitoring systems may be implemented within the same cortical network that is responsible for the primary function that has to be monitored.

Sensorimotor effects on central space representation: prism adaptation influences haptic and visual representations in normal subjects

Prism adaptation improves visual and haptic manifestations of left neglect, and can induce a small but reliable simulation of left visual neglect in normal individuals. Here, we present two experiments in which the effects of prism adaptation on the representation of space were explored. In Experiment 1, normal subjects were required to locate the centre of a haptically explored circle, before and after adaptation to leftward displacing prisms. In Experiment 2, a visual circle centring task was used. In both tasks, prism adaptation induced a significant rightward shift of performance. In addition, in both experiments, three classical measures of visuo-manual adaptation were taken: the visual shift, the proprioceptive shift and the total shift. The effects found on the haptic and visual tasks did not correlate with any of these measures. This suggests that the effects of prism adaptation on the circle centring tasks did not depend directly on the sensorimotor consequences of the adaptation. These results imply that prism adaptation can affect noetic levels of space representation in normal subjects, supporting the hypothesis that this low-level sensorimotor intervention can exert a bottom-up structuring influence on higher levels of cognitive integration.

Touch-screen system for assessing visuo-motor exploratory skills in neuropsychological disorders of spatial cognition

A new computerised test adopting touch-screen technology has been developed to assess the visuo-motor exploration of extra-personal space. The test was derived from well-known paper-and-pencil cancellation tasks used widely in the diagnosis and quantitative assessment of unilateral spatial neglect (USN), a neuropsychological syndrome that is more frequent and severe after damage to the right cerebral hemisphere. A main component deficit of USN is the defective visuo-motor exploration of the side of space contralateral to the side of the lesion (contralesional), namely, in right-sided brain-damaged patients it occurs on the left side and vice versa. The computer-based paradigm consisted of a visuo-motor spatial exploratory task: the subjects were instructed to touch, in any order they wished, all the targets they detected on a computer touch-screen. This measured the time of occurrence and the spatial co-ordinates of each touch event and forwarded the data to the computer for storage; the computer provided feedback to the subject by 'tagging' the touched target. The paradigm allowed the calculation of accuracy and latency indexes and recorded the exploratory pathway taken by each subject. A pilot study was performed in ten normal subjects and 15 brain-damaged patients, with and without psychometric evidence of USN; the results showed that the equipment was able to provide quantitative indexes related to the spatial-temporal aspects of exploratory ability, which are useful for diagnostic purposes, and revealed significant differences between the controls and patients with USN: the overall average values of latency and crossing indexes increased in patients with USN, compared with the controls (latency from 0.77 to 1.90s; path crossing index from 7.0% to 59.5%), and the significantly negative USN patient latency gradient (-2.79 against a null control value) evidenced a worsening of performance towards the left side.

Extrapersonal visual unilateral spatial neglect and its neuroanatomy

The neural correlates of left extrapersonal visual unilateral spatial neglect (VUSN), the more extensively investigated component of the neglect syndrome, are reviewed. Damage to a number of right-hemisphere regions brings about VUSN: the posterior parietal cortex (inferior parietal lobule) and, although less frequently, the premotor cortex and subcortical structures, such as the thalamus and the basal ganglia, and white matter fiber tracts. In recent years, a number of studies have investigated the possible association of specific components of left VUSN with damage to specific brain regions within the right hemisphere. The putative distinction most extensively investigated from an anatomical perspective concerns the perceptual vs premotor components of VUSN. In addition, a fine-grain componential analysis of the behavioral tasks used to investigate VUSN is providing more specific insight into the pathological mechanisms underlying the variety of its manifestations. The emerging pattern is that USN is a multifarious disorder, in which specific deficits are associated with damage localized in discrete brain regions and neural circuits. These data concur with evidence from other domains (functional neuroimaging, neurophysiology) to suggest a highly multicomponential neural and functional architecture of spatial cognition.

Cerebral representations for egocentric space: Functional-anatomical evidence from caloric vestibular stimulation and neck vibration

The internal representation of space involves the integration of different sensory inputs-visual, somatosensory/proprioceptive, vestibular-yielding reference frames which are not based on individual peripheral sensory codes, being organized instead in ego-centred (e.g. head, trunk, arm) and object- or environment-centred coordinates. Lateralized or direction-specific stimulation of peripheral sensory systems, such as caloric vestibular stimulation (CVS), posterior neck muscle mechanical vibration (NV) and optokinetic stimulation, can induce a distortion of egocentric coordinates, causing, for example, a deviation of the subjective straight ahead in pointing tasks. Appropriate forms of this stimulation can also temporarily improve a variety of pathological manifestations of unilateral neglect. We used PET measurements of regional cerebral blood flow changes in normal volunteers to measure the brain responses shared by CVS and NV. We show that somatosensory areas of the perisylvian cortex including the insula and retroinsular cortex, the temporoparietal junction and somatosensory area II receive signals from both sensory channels. We propose that these anatomical sites contribute to egocentric representation of space.

Understanding metaphors and idioms: a single-case neuropsychological study in a person with Down syndrome

The ability of subject F.F., diagnosed with Down syndrome, to appreciate nonliteral (interpreting metaphors and idioms) and literal (vocabulary knowledge, including highly specific and unusual items) aspects of language was investigated. F.F. was impaired in understanding both metaphors and idioms, while her phonological, syntactic and lexical-semantic skills were largely preserved. By contrast, some aspects of F.F.'s executive functions and many visuospatial abilities were defective. The suggestion is made that the interpretation of metaphors and idioms is largely independent of that of literal language, preserved in F.F., and that some executive aspects of working memory and visuospatial and imagery processes may play a role.

Processing of illusion of length in spatial hemineglect: a study of line bisection

Bisection of horizontal lines and of the Brentano form of the Müller-Lyer illusion was investigated in six right brain-damaged patients with left spatial hemineglect, and in six control subjects. Patients bisected the lines to the right of the objective mid-point. Comparable illusory effects on line bisection were however found in both patients and control subjects. Relative to the baseline condition, in both groups the subjective midpoint was displaced towards the side expanded by the illusion, both leftwards and rightwards. By contrast, line length and spatial position of the stimulus had differential effects. In neglect patients, the rightward bisection error increased disproportionately with line length, and when the stimulus was located in the left, neglected, side of egocentric space. Control subjects showed no such effects. The suggestion is made that the visual, non-egocentric, processes underlying these illusory effects of length may be spared in patients with left spatial neglect. The possible neural basis of this dissociation is discussed.

The neural basis of egocentric and allocentric coding of space in humans: a functional magnetic resonance study

The spatial location of an object can be represented in the brain with respect to different classes of reference frames, either relative to or independent of the subject's position. We used functional magnetic resonance imaging to identify regions of the healthy human brain subserving mainly egocentric or allocentric (object-based) coordinates by asking subjects to judge the location of a visual stimulus with respect to either their body or an object. A color-judgement task, matched for stimuli, difficulty, motor and oculomotor responses, was used as a control. We identified a bilateral, though mainly right-hemisphere based, fronto-parietal network involved in egocentric processing. A subset of these regions, including a much less extensive unilateral, right fronto-parietal network, was found to be active during object-based processing. The right-hemisphere lateralization and the partial superposition of the egocentric and the object-based networks is discussed in the light of neuropsychological findings in brain-damaged patients with unilateral spatial neglect and of neurophysiological studies in the monkey.

A fronto-parietal system for computing the egocentric spatial frame of reference in humans

Spatial orientation is based on coordinates referring to the subject's body. A fundamental principle is the mid-sagittal plane, which divides the body and space into the left and right sides. Its neural bases were investigated by functional magnetic resonance imaging (fMRI). Seven normal subjects pressed a button when a vertical bar, moving horizontally, crossed the subjective mid-sagittal plane. In the control condition, the subjects' task was to press a button when the direction of the bar movement changed, at the end of each leftward or rightward movement. The task involving the computation of the mid-sagittal plane yielded increased signal in posterior parietal and lateral frontal premotor regions, with a more extensive activation in the right cerebral hemisphere. This direct evidence in normal human subjects that a bilateral, mainly right hemisphere-based, cortical network is active during the computation of the egocentric reference is consistent with neuropsychological studies in patients with unilateral cerebral lesions. Damage to the right hemisphere, more frequently to the posterior-inferior parietal region, may bring about a neglect syndrome of the contralesional, left side of space, including a major rightward displacement of the subjective mid-sagittal plane. The existence of a posterior parietal-lateral premotor frontal network concerned with egocentric spatial reference frames is also in line with neurophysiological studies in the monkey.

Recovery of neglect after right hemispheric damage: H2(15)O positron emission tomographic activation study

BACKGROUND

The neural correlates of recovery of unilateral neglect (ULN), as well as of other consequences of focal brain damage, are largely unknown. Functional neuroimaging methods (in particular, positron emission tomography [PET]) can be applied to the in vivo study of recovery mechanisms in neurologic patients.

OBJECTIVE

To evaluate the functional cerebral correlates of recovery from ULN in patients with right-sided lesions, with the use of a PET activation paradigm.

METHODS

Study of 3 patients with cerebrovascular lesions that involved corticosubcortical (patient 1) or subcortical (patients 2 and 3) areas of the right hemisphere. Unilateral neglect was tested twice, before and after completion of a 2-month rehabilitation program, after which all 3 patients showed considerable improvement. Similarly, 2 PET examinations were performed, before and after recovery, during the performance of a visuospatial task requiring the patients to detect and respond to visual targets moving on a computer screen from the right to the left visual hemifield (experimental condition). The cerebral activation was compared with a baseline task in which subjects responded to a black dot flashing in a fixed position of the right hemifield.

RESULTS

The brain areas activated by the performance of the visuospatial task before and after recovery were compared. In all 3 patients, the regions notably more active after recovery were almost exclusively found in right-sided cortical areas and largely overlapped with those observed in a group of 4 normal subjects performing the same task. Other areas, which have been shown to be involved in attentional and oculomotor tasks in other PET studies, were also activated in patients with ULN.

CONCLUSIONS

The behavioral recovery of ULN in these patients with predominantly subcortical lesions is mainly associated with cerebral activations in cortical regions similar to those observed in normal subjects. There is some evidence of functional reorganization in individual subjects, which involves other areas related to space representation and exploration.

Motor deficits and optokinetic stimulation in patients with left hemineglect

Optokinetic stimulation with left direction of the movement of luminous dots temporarily improved motor weakness of the left hand in two right-brain-damaged patients with left spatial hemineglect. Stimulation to the right had no effect. In two left-brain-damaged patients, optokinetic stimulation did not affect the right motor weakness, regardless of direction of the movement of the optokinetic stimuli. We suggest that in patients with left hemineglect, contralesional motor deficits have a neglect-related component, which, as other aspects of the neglect syndrome, may be improved by optokinetic stimulation. The mechanisms may include a temporary restoration of the spatial coordinates of bodily representations, pathologically distorted towards the side of the lesion.

Gravitational inputs modulate visuospatial neglect

Right brain-damaged patients with left visuospatial neglect were required to bisect a line placed in front of them in two different body positions (upright and supine) and two different light conditions (light and dark). The neglect patients, unlike right brain-damaged patients without neglect, strongly reduced their rightward directional error in the supine compared with the upright position. No systematic changes were produced by the light-dark manipulation. The present result cannot be explained with an attentional interpretation of hemispatial neglect. We suggest that the present data provide further evidence that hemineglect is the consequence of a mismatch between different afferent information integrated into an egocentric space representation. According to this model, the presence of a lateralized brain lesion produces asymmetries in some intermediate spatial representations (eye-head, head-trunk, body-environment) but not in the retinotopic one. Any experimental manipulation that reduces the asymmetry of the intermediate representation such as the reduction of gravitational inputs may improve the dynamic integration of the egocentric coordinates.

Spatial frames of reference and somatosensory processing: a neuropsychological perspective

In patients with lesions in the right hemisphere, frequently involving the posterior parietal regions, left-sided somatosensory (and visual and motor) deficits not only reflect a disorder of primary sensory processes, but also have a higher-order component related to a defective spatial representation of the body. This additional factor, related to right brain damage, is clinically relevant: contralesional hemianaesthesia (and hemianopia and hemiplegia) is more frequent in right brain-damaged patients than in patients with damage to the left side of the brain. Three main lines of investigation suggest the existence of this higher-order pathological factor. (i) Right brain-damaged patients with left hemineglect may show physiological evidence of preserved processing of somatosensory stimuli, of which they are not aware. Similar results have been obtained in the visual domain. (ii) Direction-specific vestibular, visual optokinetic and somatosensory or proprioceptive stimulations may displace spatial frames of reference in right brain-damaged patients with left hemineglect, reducing or increasing the extent of the patients' ipsilesional rightward directional error, and bring about similar directional effects in normal subjects. These stimulations, which may improve or worsen a number of manifestations of the neglect syndrome (such as extrapersonal and personal hemineglect), have similar effects on the severity of left somatosensory deficits (defective detection of tactile stimuli, position sense disorders). However, visuospatial hemineglect and the somatosensory deficits improved by these stimulations are independent, albeit related, disorders. (iii) The severity of left somatosensory deficits is affected by the spatial position of body segments, with reference to the midsagittal plane of the trunk. A general implication of these observations is that spatial (non-somatotopic) levels of representation contribute to corporeal awareness. The neural basis of these spatial frames includes the posterior parietal and the premotor frontal regions. These spatial representations could provide perceptual-premotor interfaces for the organization of movements (e.g. pointing, locomotion) directed towards targets in personal and extrapersonal space. In line with this view, there is evidence that the sensory stimulations that modulate left somatosensory deficits affect left motor disorders in a similar, direction-specific, fashion.

Dissociation between position sense and visual-spatial components of hemineglect through a specific rehabilitation treatment

Current evidence suggests an association between contralesional extra-personal hemineglect, and deficits of arm position sense in patients with damage to the right cerebral hemisphere. A unitary deficit may produce both disorders, or this association may reflect the anatomical contiguity of relevant brain structures. A rehabilitation treatment, devised for visual-spatial hemineglect, was used to investigate these hypotheses in 8 patients with damage to the right cerebral hemisphere. The treatment improved hemineglect, but not the position sense deficit. The severity of the latter was however transiently reduced by optokinetic stimulation, with effects similar to those found in visual-spatial hemineglect. These effects of rehabilitation suggest that extra-personal hemineglect and the neglect-related component of the position sense disorder of the left forearm are independent, though frequently associated, deficits. Implications for the design of rehabilitation programs are discussed.

The phonological short-term store-rehearsal system: patterns of impairment and neural correlates

Two left brain-damaged patients (L.A. and T.O.) with a selective impairment of auditory-verbal span are reported. Patient L.A. was unable to hold auditory-verbal material in the phonological store component of short-term memory. His performance was however normal on tasks requiring phonological judgements, which specifically involve the phonological output buffer component of the rehearsal process. He also showed some evidence that rehearsal contributed to the immediate retention of auditory-verbal material. Patient T.O. never made use of the rehearsal process in tasks assessing both immediate retention and the ability to make phonological judgements, but the memory capacity of the phonological short-term store was comparatively preserved. These contrasting patterns of impairment suggest that the phonological store component of verbal short-term memory was severely impaired in patient L.A., and spared, at least in part, in patient T.O. The rehearsal process was preserved in L.A., and primarily defective in T.O. The localisation of the lesions in the left hemisphere (L.A.: inferior parietal lobule, superior and middle temporal gyri; T.O.: sub-cortical premotor and rolandic regions, anterior insula) suggests that these two sub-components of phonological short-term memory have discrete anatomical correlates.

Left neglect dyslexia and the processing of neglected information

A patient (ES) with a right fronto-temporo-parieto-occipital lesion, and left neglect dyslexia, is reported. ES performed reading and association tasks on written words, composed of two embedded words, one to the left and one to the right of the division point. The meaning of the whole stimulus differed from that of the embedded words, and could not be inferred from either of them. ES produced appropriate associations even to those stimuli on which she made neglect paralexic errors. This dissociation reflects a distinction between processes which use co-ordinate spatial systems and subserve perceptual awareness, impaired in hemineglect, and processes which do not. The latter analyse left-sided information to a large extent, without reaching awareness.

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.

Gravity and hemineglect

Spatial cognition requires the integration of visual inputs with proprioceptive and vestibular information about the position of the eye, the head and the body. All these sources are used by the brain to produce multiple higher-order (e.g. egocentric) representations of space, subserving accurate spatial behaviour. Such spatial representations are disrupted by unilateral cerebral damage producing neglect in the contralateral side of space. In eight brain-damaged patients with left unilateral neglect the manipulation of gravitational-otolithic information, obtained by placing patients in a supine position, produced a significant reduction of the rightward directional error in the line bisection task in all cases. This finding suggests that, in patients with neglect, gravitational information is processed in a non-symmetrical fashion, with a rightward bias towards the side of the lesion. This is the first study showing that manipulation of gravitational input affects neuropsychological disorders of visuo-spatial processing.

Optokinetic stimulation affects both vertical and horizontal deficits of position sense in unilateral neglect

The effects of optokinetic stimulation on the disorders of position sense in the horizontal and vertical planes were assessed in 24 patients with unilateral cerebral lesions (eight right brain-damaged patients with visuo-spatial hemineglect, eight right brain-damaged patients without neglect, eight left brain-damaged patients without neglect). In neglect patients, the position sense disorder was more severe, and affected by optokinetic stimulation in a direction-specific fashion. In both the horizontal and the vertical plane, and in both arms, stimulation with a direction of the movement contralateral to the side of the lesion improved the disorder, whereas stimulation with an ipsilateral direction worsened the deficit. The suggestion is made that in patients with neglect the disorder of position sense is produced, at least in part, by an ipsilateral distortion of an egocentric co-ordinate system, comprising both the horizontal and the vertical dimension, which may be affected by direction-specific optokinetic stimuli.

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.

Modulation of conscious experience by peripheral sensory stimuli

Lack of awareness of touch associated with brain damage may transiently recover after stimulation of the vestibular system. We used positron emission tomographic regional cerebral blood flow measurements to study the neurophysiological effect of vestibular stimulation on touch imperception in a subject with a right brain lesion. We tested the hypothesis that the vestibular system aids conscious tactile perception by introducing a bias in the neural system subserving body representation. We show that in normal subjects touch and vestibular signals share projections to the putamen, insula, somatosensory area II, premotor cortex and supramarginal gyrus. In our patient a subset of these regions (right putamen and insula) was spared by the lesion and was maximally active when touch and vestibular stimulations were combined. These results support the suggestion that our phenomenological consciousness is associated with activation in circumscribed brain areas specific to the particular sensation of which we are aware.

Spatial hemineglect in back space

The subjective location of the mid-sagittal plane was assessed by a free-field auditory localization task in the front and in the back half-spaces in 11 right brain-damaged patients with spatial hemineglect, 10 right brain-damaged patients without spatial hemineglect, and 11 normal control subjects. In patients with hemineglect the subjective mid-sagittal plane was found to be displaced rightwards in both half-spaces. Both patients without hemineglect and controls, in contrast, made a minor error, and showed a greater displacement towards the left side in the back half-space. In four right brain-damaged patients the rightward displacement was confined either to the front, or to the back half-space. This pattern of impairment may be explained by a rightward, ipsilesional, pathological translation of an egocentric co-ordinate system, rather than by a rotation around the vertical axis of the body.

Verbal short-term memory and vocabulary learning in polyglots

Polyglot and non-polyglot Italian subjects were given tests assessing verbal (phonological) and visuo-spatial short-term and long-term memory, general intelligence, and vocabulary knowledge in their native language. Polyglots had a superior level of performance in verbal short-term memory tasks (auditory digit span and nonword repetition) and in a paired-associate learning test, which assessed the subjects' ability to acquire new (Russian) words. By contrast, the two groups had comparable performance levels in tasks assessing general intelligence, visuo-spatial short-term memory and learning, and paired-associate learning of Italian words. These findings, which are in line with neuropsychological and developmental evidence, as well as with data from normal subjects, suggest a close relationship between the capacity of phonological memory and the acquisition of foreign languages.

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.

Identification of the central vestibular projections in man: a positron emission tomography activation study

The cerebral representation of space depends on the integration of many different sensory inputs. The vestibular system provides one such input and its dysfunction can cause profound spatial disorientation. Using positron emission tomography (PET), we measured regional cerebral perfusion with various vestibular stimulations to map central vestibular projections and to investigate the cerebral basis of spatial disorientation. We showed that the temporoparietal cortex, the insula, the putamen, and the anterior cingulate cortex are the cerebral projections of the vestibular system in man and that the spatial disorientation caused by unilateral vestibular stimulation is associated with their asymmetric activation.

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.

Immunologic changes in circulating leukocytes in the presence of atherosclerotic disease

To assess the numeric and functional changes in circulating white blood cells in the presence of severe atherosclerosis, 25 subjects with marked, angiographically assessed, atherosclerotic lesions and 29 selected controls were studied. Of the differential leukocyte counts, only monocyte count was significantly higher in the atherosclerotic than in the control subjects (449.0 +/- 115.6 (1 S.D.) vs. 344.1 +/- 138.8/mmc; P = 0.0016). By flow-cytometry no significant differences concerning monocyte surface antigens were found, except a feeble decrease in beta 2-microglobulin in the atherosclerotic subjects. As to lymphocytes, an increase in the CD8 population (33.4 +/- 6.8 vs 28.6 +/- 6.5%; P = 0.0144) and decreases in class I HLA antigen (96.6 +/- 7.3 vs 99.4 +/- 0.7%; P = 0.0049), beta 2-microglobulin (97.9 +/- 2.1 vs 99.3 +/- 1.0%; P = 0.0055) and especially in vivo DNA synthesis (3.8 +/- 1.2 vs 5.3 +/- 2.1%; P = 0.0102) percent expressions were found in the atherosclerotic patients with respect to the controls. This study shows that circulating monocytes are increased in atherosclerotic disease, possibly due to their participation in the phagocytosis of lipids in the arterial wall, with no further immunologic involvement. Conversely, the replicative activity of T lymphocytes is decreased, which might be a consequence of or a factor predisposing to atherosclerosis.

Deficits of position sense, unilateral neglect and optokinetic stimulation

The effects of optokinetic stimulation on position sense disorders were investigated in a series of 30 patients with unilateral vascular lesions (10 right brain-damaged patients with visuospatial hemineglect, 10 right brain-damaged patients without visuo-spatial hemineglect, 10 left brain-damaged patients), and 10 control subjects. The position sense deficit was more severe in right brain-damaged patients with neglect, where both the contralateral and the ipsilateral arm were involved. Optokinetic stimulation was effective only in right brain-damaged patients with neglect: stimulation with a leftward movement (contralateral to the side of the hemispheric lesion) improved the position sense deficit, while stimulation with a rightward (ipsilateral) movement produced a worsening of the performance level. These findings suggest that in right brain-damaged patients with neglect the position sense deficit has a nonsensory component, related to neglect, which may be affected by optokinetic stimulation. The role of the derangement of sensory and perceptual-egocentric representations of the body and of extrapersonal space in producing position sense disorders is discussed.

Preserved vocabulary acquisition in Down's syndrome: the role of phonological short-term memory

We report the study of a 23-year-old Italian girl, FF, with Down's syndrome (trisomy 21). FF showed a remarkably good developmental acquisition of Italian language and vocabulary and was able to learn English and French, although the latter with less proficiency. FF showed an entirely preserved function of the phonological short-term store and articulatory rehearsal components of verbal short-term memory. By contrast, she was impaired in a wide range of tasks assessing verbal and non-verbal reasoning, visuo-spatial perception and memory, and verbal long-term memory. These findings, in line with evidence from brain-damaged patients, normal subjects and children, suggest that phonological short-term memory plays a crucial role in vocabulary acquisition, which may occur in the presence of substantial deficits of general intelligence and episodic memory.

Evidence of multiple memory systems in the human brain. A [18F]FDG PET metabolic study

Patients with global amnesia of different aetiologies (n = 11), and patients with probable Alzheimer's disease of recent onset and mild to moderate severity (n = 18) underwent extensive neuropsychological examination, which included the evaluation of multiple components of memory, and a measurement of regional cerebral glucose metabolism with [18F]fluoro-deoxyglucose ([18F]FDG) and PET. In the neuropsychological tests, both global amnesia and Alzheimer's disease patients had impaired episodic long-term memory, while deficits of short-term, semantic and implicit memory were present only in Alzheimer's disease. When local metabolic rates for glucose were compared with values from age- and education-matched normal controls, a common pattern of bilateral hypometabolism was present in the hippocampus, cingulate and frontal basal cortex of both global amnesia and Alzheimer's disease patients. On the other hand, significant hypometabolism was found in the thalamus in only global amnesia, and in the frontal, parietal and temporal associative cortex in only Alzheimer's disease. The results of a multivariate regression analysis of test scores with metabolic data indicated that different clusters of cerebral areas were associated with each of the main components of memory function. These data are in agreement with 'neural network' models of the neural basis of cognition, according to which complex functions are subserved by multiple interconnected cortical and subcortical structures.

Hemianopia, hemianaesthesia, and hemiplegia after right and left hemisphere damage. A hemispheric difference

The incidence of somatosensory, visual half-field and motor deficits contralateral to a hemispheric lesion in a continuous series of 154 left brain damaged and 144 right brain damaged stroke patients were investigated. These contralateral disorders were more frequent after lesions of the right hemisphere. This difference cannot be attributed to a bias in patients' selection. It is suggested that left spatial neglect is the factor underlying this hemispheric difference.

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.

Left and right hemisphere contribution to recovery from neglect after right hemisphere damage--an [18F]FDG pet study of two cases

A 2-[18F]-Fluoro-2-Deoxy-D-Glucose ([18F]FDG) and positron emission tomography (PET) study was performed in the acute and chronic phase of stroke in one patient with unilateral neglect due to a right hemispheric lesion. In the acute phase, severe neglect, as well as hypometabolism in both the right and in the left unaffected cerebral hemisphere, was demonstrated. At follow-up evaluation the patient showed an almost complete recovery from unilateral neglect. This was associated with a return of left hemisphere metabolism to normal values and partial metabolic recovery in the right hemisphere, where frontal and parietal areas remained functionally impaired. Another patient with an extensive right cerebral ischaemic lesion on CT and severe unilateral neglect was studied by PET in chronic phase. A severe metabolic depression in the left unaffected hemisphere and in the right cerebral areas spared by the lesion, was found. These data suggest that the remission of unilateral neglect might be associated to a functional metabolic recovery in both the undamaged left hemisphere and the unaffected regions of the right hemisphere.

Increased serum IgA levels in subjects with previous myocardial infarction or other major ischemic events

To ascertain whether the increase in serum IgA, which has been found to be associated with the presence of severe atherosclerotic disease, precedes or follows the occurrence of major ischemic events (MIE), we studied the serum levels of IgA as well as IgG and IgM in 145 subjects with acute or previous ischemic events and 34 controls. The subjects with previous myocardial infarction had higher IgA levels with respect to the controls, the patients with angina pectoris and those with acute myocardial infarction, while no significant differences concerning IgG and IgM were found. In the subjects with previous extracoronary events, immunoglobulin levels tended to be even higher. Overall, 30% of the subjects with previous MIE and only 3% of the controls had IgA levels over 4.5 g/l (p = 0.0018). This study indicates that total serum IgA is a marker of previous major ischemic events (protracted immune response to denatured proteins?), rather than a factor predisposing to atherosclerosis development.

[Association of serum C3 and essential hypertension]

This study was performed to assess the possible involvement of humoral immunity in essential hypertension, independently of the presence of atherosclerotic disease, which in turn may be associated with immunologic changes. Sixty-five patients without demonstrated atherosclerotic disease were selected according to clinical and arteriographic criteria, including 23 hypertensive subjects (all pharmacologically treated) and 42 controls. Mean ages (58.7 +/- 8.3(1 S.D.) years in the controls and 57.7 +/- 7.9 years in the hypertensive subjects) and sex distribution were similar in the 2 groups. Of the main risk factors, atherosclerosis, smoking, diabetes, total cholesterol and HDL-cholesterol were equivalent, while triglycerides were higher in the hypertensive subjects than in the controls (142.6 +/- 52.7 vs. 112.6 +/- 67.7 mg/dl; p = 0.0065). In these subjects' sera the immunoglobulins IgG, IgA and IgM, and the third and fourth complement components (C3 and C4) were measured. Of these variables, only C3 was higher in the hypertensive subjects than in the controls (124.3 +/- 29.3 vs. 107.8 +/- 18.4 mg/dl; p = 0.0183). Furthermore, C3 was significantly correlated with triglycerides (tau = 0.3613; p < 0.0001), but the association with hypertension was confirmed only for C3, and not for triglycerides, by multiple logistic regression (p = 0.0142). The increase in serum C3 suggests the possible implication of humoral immunity in the pathogenesis or progression of essential hypertension.