| Name | Luigi |
| Surname | Trojano |
| Institution | Università degli Studi della Campania Luigi Vanvitelli |
| luigi.trojano@unicampania.it | |
| Address | Department of Psychology, University of Campania 'Luigi Vanvitelli', Viale Ellittico 31, 81100 Caserta, Italy |
We describe a patient with an ischemic right frontal lesion and mild left neglect who showed a systematic tendency to transpose drawings on one side of the page, which varied depending on the starting point (left or right) of his graphic productions. When not specifically cued, the patient started to draw in the ipsilesional (right) side and tended to show allochiria on the right, but occasionally, or under specific instructions, the patient started drawing from the left side and then showed a complete reversion of his spatial transpositions. To clarify the basic mechanisms underlying such a peculiar constructional phenomenon, we performed a series of experimental investigations, including extended copying tasks, a clock-marking test (to mark the position of single hours on a clock-face), and a line bisection task with progressive left-toright or right-to-left stimulus presentation. Findings suggested that "alternating" allochiria in copying and drawing from memory tasks is an epiphenomenon of a basic inability to move attention and action away from the starting point of graphic productions. The present case study, contrasted with observations on other brain-damaged patients, demonstrates that allochiria may have different neuro-cognitive bases and offers new insights for theoretical interpretations of unilateral spatial neglect.
In the present paper, we describe a neglect patient who showed allochiria in copying and drawing a clock from memory. To verify the mechanisms of allochiria in our patient, we designed an experimental investigation including two conditions: to write single hours and to copy their spatial locations, one at a time onto blank circles. The patient showed spatial transpositions in writing hours on blank dials, but did not show allochiria in the reproduction of spatial locations. These findings suggest that the patient could not represent in her mind appropriate spatial coordinates of each hour with respect to the whole clock face. These data are in contrast with findings reported in other patients and demonstrate that constructional allochiria associated with spatial neglect may derive from different causal mechanisms. Our experimental investigation has thus paved the way for a distinction between an "attentional" and a "representational" allochiria.
Mental imagery, the generation and manipulation of mental representations in the absence of sensory stimulation, is a core element of numerous cognitive processes. We investigate the cortical mechanisms underlying imagery and spatial analysis in the visual domain using event-related functional magnetic resonance imaging during the mental clock task. The time-resolved analysis of cortical activation from auditory perception to motor response reveals a sequential activation of the left and right posterior parietal cortex, suggesting that these regions perform distinct functions in this imagery task. This is confirmed by a trial-by-trial analysis of correlations between reaction time and onset, width, and amplitude of the hemodynamic response. These findings pose neurophysiological constraints on cognitive models of mental imagery.
In recent years several attempts have been made to distinguish frontotemporal dementia (FTD) from Alzheimer's disease (AD) on neuropsychological grounds; in particular, it has been suggested that FTD patients show spared spatial abilities with respect to AD patients.
We aimed at verifying whether the hemispheric specialisation for categorical/coordinate spatial judgements also applies to the spatial imagery domain by the use of whole-brain fMRI. In a block-design experiment we used the "coordinate" mental clock test, contrasting it with a "categorical" task applied to the same clock stimuli; as a control task we used a syllable counting task requiring a verbal-phonological judgement on the same material of the two imagery tasks. Our results showed that categorical and coordinate spatial judgements on imagined stimuli rely on the activation of a set of cortical areas, centred upon the superior parietal lobule (SPL) bilaterally. These regions, together with other parietal and prefrontal areas, showed a pattern of relative lateralization, with the left hemisphere being mainly activated during the categorical task and the right in the coordinate task. These data confirm the strong involvement of the SPL in spatial processing. Moreover, our findings suggest that different interconnected neural networks are activated to comply with specific test requirements, giving rise to functional imaging patterns compatible with psychological theories on hemispheric specialization.
In this article we describe a child affected by right parieto-occipital lesion due to head injury. The patient showed left hemianopia, but not unilateral spatial neglect on traditional paper-and-pencil tests and on "ecological" tests. However, his parents reported frequent collisions with obstacles on the left side. A specific test was set up: The patient had to kick down skittles put on both sides of a route traced on the floor. He kicked down 89% of skittles on the right, but only 38% on the left side. These findings are discussed in light of recent theories on unilateral neglect.
Cognitive models for developmental dyslexia are nowadays centered on the hypothesis of a specific deficit within the phonologic module of the language system. To ascertain whether defects of spatial cognition are associated with developmental reading disability, we investigated a sample of 43 school children (aged 8-9 years) found to be reading impaired during a wide screening survey for developmental dyslexia in the province of Naples, Italy. After one year all children were tested again and only 9/43 still presented reading impairment, while the remaining had achieved a variable range of spontaneous recovery. A detailed analysis was performed on all children to characterize their cognitive performances using on one hand classical conventional tests for constructional praxis, visuospatial cognition, and visuospatial memory and on the other a specific neuropsychological battery for constructional disorders. The results of our study demonstrated that children with long-lasting reading impairment exhibited normal performances on spatial cognition tasks. Moreover, one single child was found with relevant visuospatial deficits pointing to the possible existence of a visuospatial subtype for developmental dyslexia.
The present study aimed to investigate the acquisition of visuospatial and graphomotor capacities during the pre-school and early schooling years in order to follow the normal development of drawing-related abilities and spatial cognition. Eighty children aged 3-5 years, divided in four subgroups each different for a 6-month period, and 80 children aged 8-9 years were administered a neuropsychological battery for visuospatial and visuoconstructional analysis. The battery explored five cognitive domains: visual scanning, visuospatial perceptual and representational abilities, visuomotor control and graphomotor skills. Results showed that the total scores significantly improved in each group of children with respect to the previous one, but the pattern of skill acquisition was not homogeneous. We observed a gradient from explorative and visuomotor to perceptive, representational and graphomotor abilities. Explorative and visuomotor abilities were almost mature at a time when visuoperceptual capacities began to develop. On the contrary, at that time we found very low performances at representational and constructional tasks. Our findings could suggest that constructional abilities need both perceptual and representational competences to develop properly.
Do spatial operations on mental images and those on visually presented material share the same neural substrate? We used the high spatial resolution of functional magnetic resonance imaging to determine whether areas in the parietal lobe that have been implicated in the spatial transformation of visual percepts are also activated during the generation and spatial analysis of imagined objects. Using a behaviourally controlled mental imagery paradigm, which did not involve any visual stimulation, we found robust activation in posterior parietal cortex in both hemispheres. We could thus identify the subset of spatial analysis-related activity that is involved in spatial operations on mental images in the absence of external visual input. This result clarifies the nature of top-down processes in the dorsal stream of the human cerebral cortex and provides evidence for a specific convergence of the pathways of imagery and visual perception within the parietal lobes.
Five neglect patients without diffuse cognitive impairment or overt constructional disabilities were asked to bisect lines and rectangles and to copy rectangles bisected in their midplane. As a group, patients showed the usual rightward bias in bisecting lines and a milder deviation in bisecting horizontally-aligned rectangles, but showed a leftward deviation of the subjective midline in the copying task. This was due to drawing the left half shorter with respect to normal controls but three patients also drew the right half longer (the total length was the same as that of controls). A possible interpretation of rectangle copying results in these three patients is that they could create a representation of the stimulus to be copied accurately enough to reproduce its total length correctly but the subjective distribution of right and left space within that representation was unbalanced. However, specific experimental work is needed to verify why our patients with mild to moderate unilateral spatial neglect overrepresented the left side in a line bisection task and underrepresented it in a copying task.