Sight and sound of actions share a common neural network.

The mirror-neuron system (MNS) connects sensory information that describes an action with a motor plan for performing that action. Recently, studies using the repetition-suppression paradigm have shown that strong activation occurs in the left premotor and superior temporal areas in response to action-related, but not non-action-related, stimuli. However, few studies have investigated the mirror system by using event-related potentials (ERPs) and employing more than one sensory modality in the same sample. In the present study, we compared ERPs that occurred in response to visual and auditory action/non-action-related stimuli to search for evidence of overlapping activations for the two modalities. The results confirmed previous studies that investigated auditory MNS and extended these studies by showing that similar activity existed for the visual modality. Furthermore, we confirmed that the responses to action- and non-action-related stimuli were distinct by demonstrating that, in the case of action-related stimuli, activity was restricted mainly to the left hemisphere, whereas for non-action-related stimuli, activity tended to be more bilateral. The time course of ERP brain sources showed a clear sequence of events that subtended the processing of action-related stimuli. This activity seemed to occur in the left temporal lobe and, in agreement with findings from previous studies of the mirror-neuron network, the information involved appeared to be conveyed subsequently to the premotor area. The left temporo-parietal activity observed following a delay might reflect processing associated with stimulus-related motor preparation.

Does outcome of neuropsychological treatment in patients with unilateral spatial neglect after stroke affect functional outcome?

BACKGROUND: Unilateral spatial neglect (USN) after stroke is associated to severe disability and to a poor rehabilitation outcome. However it is still unclear if a reduction of USN after a specific neurophsycological treatment could also favor the functional recovery. AIM: The first aim of this study was to determine if low responders to neuropsychological treatment of unilateral spatial neglect may have a worse functional prognosis for activities of daily living. The second aim was to investigate which variables can predict a low response to neuropsychological treatment. DESIGN: Observational study. SETTING: Neurorehabilitation hospital in Italy. POPULATION: Two hundred inpatients with the diagnosis of ischemic stroke were screened in this observational study. Inclusion criteria were: patients in subacute phase of first ischemic stroke in right hemisphere. Exclusion criteria were: presence of previous and/or other disabling pathologies, medical conditions contraindicating physical therapy. Data of 73 patients who performed neurorehabilitation and visual scanning training for reducing USN were analysed, while the remaining others were excluded for at least one of the following reasons: hemorrhagic lesions, presence of other chronic disabling pathologies, contraindications for therapy. METHODS: USN was evaluated using: Letter Cancellation Test, Barrage Test, Sentence Reading Test and Wundt-Jastrow Area Illusion Test. Barthel Index (BI), Beck Depression Inventory, and Canadian Neurological Scale were also administered. According to the aim of the study, forward binary logistic regressions were performed to evaluate the effects of different factors on functional recovery. RESULTS: Three factors were identified as predictors of low effectiveness in terms of BI-score: older age (odds ratio OR=9.882, P=0.002), severity of disease at admission (OR=12.594, P=0.002) and being low responders to neuropsychological treatment (OR=3.847, P=0.027). Further, the initial barrage score (OR=3.313, P=0.027) and the initial BI-score (OR=3.252, P=0.039) effectively predict the response to neuropsychological treatment. CONCLUSION: The outcome of the whole rehabilitation resulted affected by the outcome of neuropsychological treatment in patients with USN, being a low score at Barrage test at the beginning of therapy a negative predictor of USN recovery. CLINICAL REHABILITATION IMPACT: Patients with USN after stroke can benefit of a specific training for reducing USN also in terms of functional outcome. Further, the simple use of Barrage test could provide important prognostic information about recovery.

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.

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.

The Wundt-Jastrow illusion in the study of spatial hemi-inattention.

A new test to detect unilateral neglect was devised using a modified version of the Wundt-Jastrow area illusion. The test was given to three groups of subjects: left brain damaged (LBD), right brain damaged (RBD) patients and controls. Of RBD patients, 40.4% but no LBD patient or control, showed responses inconsistent with the visual illusion when the determinant features of the illusion pointed to the left visual field. These unexpected responses were highly related to a clinical evaluation of the severity of the hemi-inattention disorder. The sensitivity of this test and of other standard measures of hemi-neglect were compared. The possibility of identifying qualitatively different forms of hemi-neglect was also discussed.

Contrast sensitivity and low spatial frequency discrimination in hemi-neglect patients.

Contrast sensitivity for sinusoidal gratings of different spatial frequencies and low spatial frequency discrimination of high contrast squarewave gratings were measured in 26 right brain damaged patients, 15 of whom showed symptoms of spatial hemi-neglect. No difference was present between neglect and non-neglect patients in either task. A difference in contrast sensitivity restricted to low spatial frequencies was present between controls and patients, independent of neglect. Overall, results indicated that spatial vision at threshold and suprathreshold levels is not selectively impaired in patients with hemi-neglect, a finding consistent with theories which postulate a post-perceptual locus of impairment in this syndrome.

Transcutaneous electrical stimulation of the neck muscles and hemineglect rehabilitation.

In four patients with left visuo-spatial hemineglect and right brain- damage, the therapeutic effects of Transcutaneous Electrical Nervous Stimulation (TENS) of the left neck muscles, associated with a non-specific treatment, and of a specific rehabilitation paradigm were investigated. The two treatments were given for an 8-week period each. TENS had positive effects on hemineglect in two out of four patients, whereas the specific treatment produced a major improvement of the disorder in all four cases. The suggestion is made that an effective treatment of neglect requires a paradigm comprising a range of visuo-spatial exploratory tasks of increasing complexity and a systematic feedback as to the success of the patients' performance. This is the case of the specific treatment. By contrast a procedure confined to a sensory stimulation, which produces a short-term improvement in the range of minutes, does not have comparable long-term effects. © 1996 Elsevier Science Ireland Ltd. All rights reserved.

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.

TENS modulates spatial reorientation in neglect patients.

The existence of separate systems for processing geometric and non-geometric spatial information was studied. Twelve neglect patients were asked to reorient themselves in a room using only geometric information or to integrate this information with relevant visual cues both in the presence and in the absence of transcutaneous electrical neural stimulation (TENS). In the absence of TENS, all patients were greatly impaired in coding geometric information, and they had difficulty in coding non-geometric information. TENS significantly improved the ability to code shape-based representation, but is ineffective with non-geometric representations (such as color). The data support previous findings on neglect patients suggesting the presence of separate, independent neural systems subserving different types of space representation.

Disappearance of leftward rapid eye movements during sleep in left visual hemi-inattention.

Contrasting hypotheses have been proposed about the functional equivalence between waking saccades and REMs. Patients with left visual hemi-inattention showed dissociation between the direction of waking saccades and that of REMs. REMs directed toward the left were virtually absent, while waking inspective saccades directed in both lateral directions were present, but confined to the right hemispace. It is concluded that: a) the cortical areas regulating attention are relevant in the production of REMs; b) two separate attentional mechanisms have to be considered in relation to the hemi-inattentive syndrome, one is involved in the cognitive control of visual exploration and plays little or no role in the modulation of REMs, the other deals with REMs during sleep and with reflex-like orienting responses to peripheral stimuli during waking.

Amplitude and speed change of the optokinetic response in patients with and without neglect.

The present study quantitatively investigated the slow and quick phases of optokinetic nystagmus (OKN) in four groups of patients: right unilateral brain-damaged patients with neglect, left and right patients without neglect or hemianopia and patients with left or right retrogeniculate lesions and lateral homonymous hemianopia. Our results indicate that only neglect patients show a perturbation of both components of OKN. A comparison among MRI images of different patients shows that a region involving area 37 and adjacent areas 39 and 19, was impaired in all patients with neglect, but not in any other patient with either right or left lesions.

Hemiretinal differences in the effect of a rotating visual background on the subjective visual vertical.

Sixteen normal subjects were tested for their accuracy in judging the verticality of a visual edge before or during exposure to a moving visual background. All subjects showed a counter-rotation of the subjective visual vertical as a consequence of movement of the visual background. The effect was stronger for binocular than monocular viewing and for nasal than temporal hemiretina stimulation. No hemispheric asymmetries were observed. These results show a predominance of the crossed visual pathways originating from the nasal hemiretinae in a visual effect presumably involving a visual-vestibular interaction.

Patterns of lateralization and performance levels for verbal and spatial tasks in congenital androgen deficiency.

The effects of congenital deficiency of gonadal hormones on verbal and spatial performance and on the establishment of hemispheric asymmetries were investigated in a group of patients with idiopathic hypogonadotropic hypogonadism. The patients showed a left hemispheric advantage for verbal material and were mildly impaired, mainly on tasks involving a short-term memory load, in comparison with a matched control group. These results do not indicate a specific role of gonadal hormones on the establishment of hemispheric asymmetries. Lack of exposure during brain development results in a decrease in memory functions which is not specific for verbal or spatial material.

Facilitatory effect of neglect rehabilitation on the recovery of left hemiplegic stroke patients: a cross-over study.

A study of the effect of specific training for visual neglect on the recovery of motor and functional impairment in stroke patients is reported. Two groups of right hemisphere stroke patients with hemispatial neglect and one group without neglect were assessed by means of three functional and neurological scales (Rivermead Mobility Index, Barthel Index, Canadian Neurological Scale). Three evaluations were made at 0, 2 and 4 months from the beginning of physical rehabilitation. During the first 2 months of physical rehabilitation one of the two groups of neglect patients was randomly assigned to specific training for neglect, and the second group to a general cognitive intervention; during the final 2 months of rehabilitation the types of training were switched in the two groups. The non-neglect patients improved steadily during physical rehabilitation. In contrast, the functional recovery of the two neglect groups was time-locked to the period of the specific training for neglect. At the time of admission, the two neglect groups performed at the same level; after 2 months of rehabilitation, the group with neglect training showed higher functional recovery than the group with only general cognitive intervention. When the latter group received neglect training, there was no longer any difference between the two neglect groups. This pattern was present for both of the functional scales used but not for the neurological scale. Motor and functional recovery of stroke patients with neglect seems to be significantly improved by the simultaneous presence of a treatment specifically focused on neglect.

Sex and cognitive influence on visual hemifield superiority for face and letter recognition.

Two groups of field independent individuals (one M and one F) and two groups of field dependent individuals (one M and one F) were selected as subjects in the experiment. The classification of field dependence-independence was based on predetermined RFT and EFT standards. The subjects, all right-handed, were given a face and a letter recognition task in a tachistoscopic visual hemifield paradigm; reaction time with either hand was the dependent measure. field independent subjects of both sexes showed a clear right-field superiority for letter and a left-field superiority in both letter and face recognition, although of a smaller magnitude than the previous group. The results of the experiment do not support previous findings of no field superiority in females for face recognition; on the contrary, they provide additional evidence that measures of cognitive style significantly predict hemispheric specialization.

Evidence for separate allocentric and egocentric space processing in neglect patients.

Spatial orientation was investigated in two different conditions: (a) when the shape of the enclosure was the only available information; (b) when a clearly perceivable visual cue was added. Three groups of subjects were investigated: normal controls, right brain-damaged patients without and with hemispatial neglect. The performance of the first two groups clearly demonstrated the capacity to use the geometric properties of the environment and to integrate this information with an additional visual cue. Considered as a group, patients with hemispatial neglect were able to use the shape of the environment and, to a lesser extent, the additional visual cue. However, individual differences suggest two opposite performance patterns: two patients responded randomly when the shape of the environment was the only available information, and they improved considerably when the cue was offered; two other patients showed normal competence in dealing with the geometrical properties of the environment, but were unable to take advantage of the cue. The different lesion site in these two types of patients suggests a possible dissociation of processing based upon allocentric or egocentric coding of space in humans as well as in animals.

Response of the cortically blind hemifields to a moving visual scene.

Viewing a rotating field induces a counter-rotating tilt of the subjective vertical in normal subjects. A similar, though smaller, effect is observed when only one hemifield is stimulated. This technique was used with 7 hemianopic patients having retrogenicular lesions. It was hypothesized that the stimulation of a moving scene in the blind field produces an additional tilting effect to that produced by the stimulation of the normal hemifield alone. The visual rotation within only the blind field is expected to have a systematic tilting effect. Both predictions were confirmed in all 7 patients having either right or left hemianopic disorders.

Somatosensory stimulation improves imagery disorders in neglect.

A group of 9 right brain damaged patients with unilateral neglect performed a set of tasks involving mental imagery with and without a transcutaneous electrical neural stimulation (TENS) to both sides of the neck. Results showed that TENS on the left side of the neck produced significant improvements of performances on the left side of mental representations of objects (drawing, shape comparison) as well as on left side of mental images of space (description of squares). The results suggest that the modification induced by TENS may affect the imagery systems involved in objects as well as in space representation.

The contribution of functional neuroimaging to recovery after brain damage: a review.

The introduction of functional neuroimaging techniques has contributed to understanding the neural correlates of recovery of motor, sensory and cognitive functions after brain damage. In this paper, we review the literature of the past twenty years, with particular emphasis on quantitative studies of cerebral blood flow and metabolism. Studies are presented that examine recovery from hemiparesis, aphasia, spatial hemineglect and sensory disorders. The contribution of this research is critically discussed in a methodological perspective. A basic distinction is made between cerebral plasticity and recovery of functions. It is also argued that the most frequently used experimental designs do not permit directly relating changes in brain activity to functional recovery. The importance of accurate behavioural measures is underlined. Alternative experimental designs are proposed, based on correlations between behavioural performance and brain activations.