Effect of prism adaptation on left dichotic listening deficit in neglect patients: glasses to hear better?

Unilateral neglect is a disabling syndrome frequently observed following right hemisphere brain damage. Symptoms range from visuo-motor impairments through to deficient visuo-spatial imagery, but impairment can also affect the auditory modality. A short period of adaptation to a rightward prismatic shift of the visual field is known to improve a wide range of hemispatial neglect symptoms, including visuo-manual tasks, mental imagery, postural imbalance, visuo-verbal measures and number bisection. The aim of the present study was to assess whether the beneficial effects of prism adaptation may generalize to auditory manifestations of neglect. Auditory extinction, whose clinical manifestations are independent of the sensory modalities engaged in visuo-manual adaptation, was examined in neglect patients before and after prism adaptation. Two separate groups of neglect patients (all of whom exhibited left auditory extinction) underwent prism adaptation: one group (n = 6) received a classical prism treatment ('Prism' group), the other group (n = 6) was submitted to the same procedure, but wore neutral glasses creating no optical shift (placebo 'Control' group). Auditory extinction was assessed by means of a dichotic listening task performed three times: prior to prism exposure (pre-test), upon prism removal (0 h post-test) and 2 h later (2 h post-test). The total number of correct responses, the lateralization index (detection asymmetry between the two ears) and the number of left-right fusion errors were analysed. Our results demonstrate that prism adaptation can improve left auditory extinction, thus revealing transfer of benefit to a sensory modality that is orthogonal to the visual, proprioceptive and motor modalities directly implicated in the visuo-motor adaptive process. The observed benefit was specific to the detection asymmetry between the two ears and did not affect the total number of responses. This indicates a specific effect of prism adaptation on lateralized processes rather than on general arousal. Our results suggest that the effects of prism adaptation can extend to unexposed sensory systems. The bottom-up approach of visuo-motor adaptation appears to interact with higher order brain functions related to multisensory integration and can have beneficial effects on sensory processing in different modalities. These findings should stimulate the development of therapeutic approaches aimed at bypassing the affected sensory processing modality by adapting other sensory modalities.

Looking while imagining: the influence of visual input on representational neglect.

BACKGROUND: Subjects with hemispatial neglect often exhibit representational neglect: a failure to report details from the left side of mentally visualized images. This failure could reflect impaired ability to generate the left side of the mental image, or it could reflect failure to explore the left side of a normally generated mental image. When subjects with hemispatial neglect look at pictures or drawings, their attention tends to be drawn to objects on the right side, thereby aggravating their failure to explore the left side. If representational neglect represents a failure to explore the left side of a normally generated mental visual image, then it should be improved by blindfolding, which removes the attention-catching right-sided stimuli. However, if representational neglect represents a failure to generate the left side of the mental visual image, then blindfolding should have little impact on reporting of details of the image. METHODS: To determine which of these explanations is correct, we asked eight normal participants and eight brain-damaged patients with left representational neglect to imagine the map of France and to name as many towns as possible in 2 minutes. In different sessions, participants performed the task with eyes open or while blindfolded. RESULTS: Normal participants mentioned more towns while blindfolded than with vision, thus suggesting a distracting effect of visual details on mental imagery. Patients with neglect, however, showed no appreciable effect of blindfolding on reporting of details from either side of mental images. CONCLUSION: Representational neglect may represent a failure to generate the left side of mental images.

Visually guided reaching: bilateral posterior parietal lesions cause a switch from fast visuomotor to slow cognitive control.

The visually guided reaching of two patients with bilateral optic ataxia was explored in two experiments. In Experiment 1 simple delayed pointing was compared with immediate pointing. In the immediate pointing task both variable and constant errors increased with target eccentricity. In contrast to the performance of control subjects and contrary to their own beliefs, the patients both showed improved accuracy in the delay condition. This improvement was manifest as a reduction in both pointing variability and in the constant angular error towards the point of fixation. Both angular errors and their improvement with the delay were proportional to target eccentricity. Experiment 2 used a task in which the target was pre-viewed 5s prior to its re-exposure for pointing ('delayed real pointing'). On some trials a conflict was introduced between the present and previous visual information by changing the target's location during the delay. In contrast to control subjects, who ignored the pre-viewed location and aimed directly at the current target, both patients with optic ataxia initiated their movements towards the previously viewed target location. Evidently they relied on off-line information in preference to on-line visual information. In addition, the patients often failed to detect the changes in target location. One of the patients sometimes even guessed incorrectly that the target had changed its location, and her movement trajectory was then more affected by her false belief than by the target's actual location. These findings confirm that posterior parietal lesions severely disrupt direct visuomotor transformations, and suggest that the residual performance is mediated indirectly by expectations or beliefs about target position.

Bilateral vestibular stimulation does not improve visual hemineglect.

This work compared the effect of unilateral (right and left) and bilateral vestibular stimulation in a right-brain-damaged patient with neglect. Neglect was improved following left caloric vestibular stimulation, and worsened following right vestibular stimulation. On the other hand, no modification of neglect was observed after bilateral vestibular stimulation. These results support the idea that caloric vestibular stimulation may improve neglect through a specific effect; bilateral stimulation making the putative activation bilateral and symmetrical does not affect the lateral bias of neglect.

Prism adaptation improves representational neglect.

Previous work has shown that various symptoms of unilateral neglect, including the pathological shift of the subjective midline to the right, may be improved by a short adaptation period to a prismatic shift of the visual field to the right. We report here, in two neglect patients the improvement of imagery neglect after prism exposure. Despite a strong neglect observed for mental images, as well as for conventional tests, the mental evocation of left-sided information from an internal image of the map of France was fully recovered following prism adaptation to the right. This improvement could not be explained by the alteration of visuomotor responses induced by the prism adaptation. Therefore, prism adaptation may act not only on sensory-motor levels but also on a higher cognitive level of mental space representation and/or exploration.

Implicit processing of somaesthetic information: a dissociation between where and how?

We present the case of a patient with a lesion of the thalamus who was completely anaesthetized on his right side. He was unable to detect and describe a tactile stimulus applied to his affected right arm, but could direct his normal left hand toward the specific right hand site where the stimulus had been applied when so instructed ('blind touch'). Strikingly, this pointing ability disappeared when the patient had to indicate on a picture of an arm where the stimulus was applied, and when he had to name the stimulus location during his pointing. Similar results were also obtained for localizing the unfelt fingertip ('blind proprioception'). Neuropsychological case studies have demonstrated that brain lesions can produce reciprocal dissociations between object identification (what is the object) and object-oriented action (how to direct a movement to the object). Along these lines, it is suggested that our patient exhibited a dissociation between a 'where' system and a 'how' system for tactile and proprioceptive stimuli.

Effect of brain and spinal cord injuries on motor imagery.

The timing of mentally executed movements was measured in ten patients with hemiplegia, tetraplegia and paraplegia. In hemiplegic patients a significant difference in mental duration times was found between the paralysed and the normal "represented limb". The paralysed limb was mentally much slower than the healthy one. In contrast, movement times in tetraplegic and paraplegic patients did not differ from those in normal subjects. All patients reported a sensation of subjective effort accompanying the execution of the mental tasks. These observations are compatible with an outflow processing underlying motor imagery.

[Hypothalamic insufficiency following irradiation. Late, subacute and curable dementia]. / Insuffisance hypothalamique après irradiation. Démence tardive, subaiguë et curable.

A 31 year-old patient suffered from a subacute and major dementia, sixty months after whole brain irradiation with 54 grays for a pinealoma. Clinical features and biological investigations led to a diagnosis of hypothalamic insufficiency. A dramatic clinical recovery followed therapy with hydrocortisone and thyroxine. An hypothalamic radionecrosis and a vascular mechanism are presumed.

[Paralysis of downward gaze and chronic global amnesia as a result of a bilateral thalamo-subthalamic lesion]. / Paralysie de l'abaissement du regard et amnésie globale durables par lésion thalamo-sous-thalamique bilatérale.

A 47 year-old male was found in coma and upon awakening 36 hours later, he showed a selective paralysis of downward gaze and convergence associated to an intellectual impairment. He was euphoric, unconcerned, poorly attentive, and had a severe amnesia for both anterograde and retrograde material. CT scan and NMR demonstrated a bilateral lacunar lesion of thalamic and subthalamic paramedian region. Over the 5 years follow-up, behavioral, personality and amnestic changes remained. On the other hand, supranuclear gaze paralysis improved as documented by EOG recordings with persisting limitations in voluntary down movements amplitude and dramatic reduction of fast components velocity.

[Treatment of spastic foot by selective neurotomy of the tibial nerve. Results of a series of 31 cases]. / Traitement du pied spastique par la neurotomie sélective du nerf tibial. Résultats sur une série de 31 cas.

A large number of patients suffering from various neurological diseases remain disabled because of spastic disorders in their foot. These disorders--which are responsible for abnormal postures and painful disturbances for walking and standing--can be corrected by an effective procedure: the so-called Selective Neurotomy of the Tibial Nerve (T.N.), developed in its modern form by Gros in 1972. The procedure aims at sectioning the T.N. branches corresponding to the muscles, the spasticity of which is considered harmful, i.e. the soleus (and/or gastrocnemius) nerves for equinus and ankle clonus, the posterior tibialis branch for varus, and the flexor fascicles for tonic flexion of the toes. After dissection of each T.N. branches at the lower part of the popliteal region and their identification with bipolar electro-stimulation, the selected nerves are sectioned partially (about two-third of their caliber) under the operative microscope. The present series consists of 37 operations--performed 25 times unilaterally and 6 bilaterally--in 31 patients, 17 to 68 year old (39 on average). In 11 patients spasticity was from spinal cord origin and in the 20 others from vascular or traumatic cerebral damages. The spastic disorders--installed for 2 to 17 years (4 on average)--were due to one, several or all the following components: equinus, ankle clonus, varus, flexion of the toes. Surgery obtained complete suppression of the disabling spastic components, total pain relief and consequently improvement of the residual voluntary movements by achieving balance between agonist and antagonist muscles, in 33 out of the 37 cases, i.e. in 91% of the patients.(ABSTRACT TRUNCATED AT 250 WORDS)