A single case study

As in line bisection, in time bisection, neglect patients fail to process the first/left part of time representation (Mental-Time-Line-MTL) resulting in a rightward shift of the interval midpoint. A leftward shift of spatial attention after one session of prismatic-adaptation (PA) reduces this deficit. The impact on daily life of time deficit is little investigated in neglect. Here we study the time deficit and its ecological impact in an outpatient with neglect (LL) and the effects of a PA-treatment (ten sessions) on the deficit and its impact. Before and after PA-treatment, LL completed a: time-bisection-task assessing the MTL in the milliseconds-seconds range; lifespan-task assessing the MTL in the lifespan range; qualitative interview assessing the impact on daily routines. Patient's performance on the tasks was compared with the performance of non-neurological controls. Before PA-treatment, LL showed a rightward shift in the time-bisection-task and a compression of life events distribution in the lifespan-task. The feeling "to be forward in time" emerged in the interview. The PA-treatment reduced the deficits in the tasks and the feeling "to be forward in time" in the interview. PA-treatment is suggested as a powerful instrument for the reduction of time deficit and its ecological impact in neglect patients.

Multisensory stimulation for the rehabilitation of unilateral spatial neglect

Unilateral spatial neglect (USN) is a neuropsychological syndrome, typically caused by lesions of the right hemisphere, whose features are the defective report of events occurring in the left (contralesional) side of space and the inability to orient and set up actions leftwards. Multisensory integration mechanisms, largely spared in USN patients, may temporally modulate spatial orienting. In this pilot study, the effects of an intensive audio-visual Multisensory Stimulation (MS) on USN were assessed, and compared with those of a treatment that ameliorates USN, Prismatic Adaptation (PA). Twenty USN stroke patients received a 2-week treatment (20 sessions, twice per day) of MS or PA. The effects of MS and PA were assessed by a set of neuropsychological clinical tests (target cancellation, line bisection, sentence reading, personal neglect, complex drawing) and the Catherine Bergego Scale for functional disability. Results showed that MS brought about an amelioration of USN deficits overall comparable to that induced by PA; personal neglect was improved only by MS, not by PA. The clinical gains of the MS treatment were not influenced by duration of disease and lesion volume, and they persisted up to one month post-treatment. In conclusion, MS represents a novel and promising rehabilitation procedure for USN.

Investigating prismatic adaptation effects in handgrip strength and in plantar pressure in healthy subjects

BACKGROUND

Prismatic Adaptation (PA) is a visuomotor procedure inducing a shift of the visual field that has been shown to modulate activation of a number of brain areas, in posterior (i.e. parietal cortex) and anterior regions (i.e. frontal cortex). This neuromodulation could be useful to study neural mechanisms associated with either postural measures such as the distribution of plantar pressure or to the generation of muscle strength. Indeed, plantar pressure distribution is associated to activation of high-level cognitive mechanisms taking place within the posterior regions of the brain dorsal stream, especially of the right hemisphere. Conversely, hand force mostly rely on sensorimotor mechanisms, fulfilled by anterior regions of the brain and involving both hemispheres.

RESEARCH QUESTION

Since PA effects have been reported to affect both sensorimotor and higher level cognitive processes, is it possible to hypothesize a modulation of both hands strenght and plantar pressure after PA?

METHODS

Forty-six healthy subjects (male = 23; mean age = 25 ± 3 years) were randomly divided into two groups: a leftward prismatic adaptation group (l-PA) and a rightward prismatic adaptation group (r-PA). Hand strength and plantar pressure were assessed, immediately before and after PA, using the handgrip task and baropodometric measurement, respectively.

RESULTS

Both l-PA and r-PA induced a significant decrease of strength in the hand contralateral to the lenses deviation side. Only r-PA was associated with an increase of the forefoot plantar pressure in both feet. Modulation of interhemispheric inhibitory processes at sensorimotor and higher cognitive level may account for the present results.

SIGNIFICANCE

PA exerts effects on body posture and hand strength relying on different mechanisms. The PA effects on hand strength are probably related to the modulation of interhemispheric inhibition of sensorimotor processes, involving both hemispheres. The PA effects on body posture are probably related to modulation of body representation, involving mainly the right hemisphere.

Supramodal effect of rightward prismatic adaptation on spatial representations within the ventral attentional system

Rightward prismatic adaptation (R-PA) was shown to alleviate not only visuo-spatial but also auditory symptoms in neglect. The neural mechanisms underlying the effect of R-PA have been previously investigated in visual tasks, demonstrating a shift of hemispheric dominance for visuo-spatial attention from the right to the left hemisphere both in normal subjects and in patients. We have investigated whether the same neural mechanisms underlie the supramodal effect of R-PA on auditory attention. Normal subjects underwent a brief session of R-PA, which was preceded and followed by an fMRI evaluation during which subjects detected targets within the left, central and right space in the auditory or visual modality. R-PA-related changes in activation patterns were found bilaterally in the inferior parietal lobule. In either modality, the representation of the left, central and right space increased in the left IPL, whereas the representation of the right space decreased in the right IPL. Thus, a brief exposure to R-PA modulated the representation of the auditory and visual space within the ventral attentional system. This shift in hemispheric dominance for auditory spatial attention offers a parsimonious explanation for the previously reported effects of R-PA on auditory symptoms in neglect.

Combining tDCS with prismatic adaptation for non-invasive neuromodulation of the motor cortex

BACKGROUND

Prismatic adaptation (PA) shifts visual field laterally and induces lateralized deviations of spatial attention. Recently, it has been suggested that prismatic goggles are also able to modulate brain excitability, with cognitive after-effects documented even in tasks not necessarily spatial in nature.

OBJECTIVE

The aim of the present study was to test whether neuromodulatory effects obtained from tDCS and prismatic goggles could interact and induce homeostatic changes in corticospinal excitability.

METHODS

Thirty-four subjects were submitted to single-pulse transcranial magnetic stimulation (TMS) over the right primary motor cortex to measure Input-Output (IO) curve as a measure of corticospinal excitability. Assessment was made in three experimental conditions: before and after rightward PA and anodal tDCS of the right motor cortex; before and after rightward PA; before and after anodal tDCS of the right motor cortex.

RESULTS

A significant decrease of MEPs amplitude and of IO curve slope steepness was found after the combination of rightward PA and anodal tDCS; on the other hand, an increase of MEPs amplitude and of the steepness of IO curve slope on the right motor cortex was found following either rightward PA or anodal tDCS.

CONCLUSION

These findings suggest that priming of motor cortex excitability using PA could be an additional tool to modulate cortical metaplasticity.

Oculomotor prismatic training is effective in ameliorating spatial neglect: a pilot study

Visuomotor prismatic training has been demonstrated to be among the most effective rehabilitative techniques of spatial neglect, a neurological syndrome manifested by a number of right brain-damaged patients characterized by unawareness of the egocentric left half of the world. In the present study, we demonstrate that a novel oculomotor prismatic training procedure only consisting in a sequence of gaze shifts to visual targets, can reduce spatial neglect symptoms. Following oculomotor prismatic training, patients show a significant decrease in neglect severity in straight ahead and paper and pencil tasks. We propose that during oculomotor prismatic training, the inconsistency between the prisms-biased visual/oculomotor input and the unbiased head-on-trunk proprioceptive information relative to the straight-ahead position determines the observed aftereffects and the amelioration of spatial neglect symptoms.

Hypnotizability and Performance on a Prism Adaptation Test

The susceptibility to hypnosis, which can be measured by scales, is not merely a cognitive trait. In fact, it is associated with a number of physiological correlates in the ordinary state of consciousness and in the absence of suggestions. The hypnotizability-related differences observed in sensorimotor integration suggested a major role of the cerebellum in the peculiar performance of healthy subjects with high scores of hypnotic susceptibility (highs). In order to provide behavioral evidence of this hypothesis, we submitted 20 highs and 21 low hypnotizable participants (lows) to the classical cerebellar Prism Adaptation Test (PAT). We found that the highs' performance was significantly less accurate and more variable than the lows' one, even though the two groups shared the same characteristics of adaptation to prismatic lenses. Although further studies are required to interpret these findings, they could account for earlier reports of hypnotizability-related differences in postural control and blink rate, as they indicate that hypnotizability influences the cerebellar control of sensorimotor integration.

Prisms to travel in time: Investigation of time-space association through prismatic adaptation effect on mental time travel

Accumulating evidence suggests that humans process time and space in similar veins. Humans represent time along a spatial continuum, and perception of temporal durations can be altered through manipulations of spatial attention by prismatic adaptation (PA). Here, we investigated whether PA-induced manipulations of spatial attention can also influence more conceptual aspects of time, such as humans' ability to travel mentally back and forward in time (mental time travel, MTT). Before and after leftward- and rightward-PA, participants projected themselves in the past, present or future time (i.e., self-projection), and, for each condition, determined whether a series of events were located in the past or the future with respect to that specific self-location in time (i.e., self-reference). The results demonstrated that leftward and rightward shifts of spatial attention facilitated recognition of past and future events, respectively. These findings suggest that spatial attention affects the temporal processing of the human self.