| Name | Dario |
| Surname | Grossi |
| Institution | Università degli Studi della Campania Luigi Vanvitelli |
| dario.grossi@unicampania.it | |
| Address | Villa Camaldoli Foundation Clinic, Naples, Italy; Department of Psychology, University of Campania "Luigi Vanvitelli", Napoli, Italy |
Using repetitive transcranical magnetic stimulation (rTMS), we investigated the functional relevance of posterior parietal cortex for categorical and coordinate judgements in the spatial imagery domain. In the coordinate task, subjects were asked to imagine two analogue clock faces based on acoustically presented pairs of times, and to judge at which of the two times the clock hands form the greater angle (mental clock task); in the categorical task subjects were again asked to imagine an analogue clock face showing the time verbally presented by the examiner, but in this case they had to judge whether both hands lay in the half of the clock face cued by an auditorily presented label. We matched the performance of three groups of subjects, two of which received rTMS stimulation over left and right posterior parietal cortex, respectively, while the third group received a sham stimulation. The results showed that right parietal stimulation interfered with the execution of the coordinate task, while left parietal stimulation mainly affected the categorical task, but also reduced the learning effect on the coordinate task. The present findings support the hemispheric specialization of the posterior parietal cortex in different spatial information processing in the imagery domain.
Hallucinations occur in patients with Parkinson's disease (PD) with reported prevalence ranging from 8% to 40%. Hallucinations are significantly associated with dementia in PD, but little is known about possible distinctive cognitive features of non-demented PD patients who develop hallucinations.
The authors report a patient with a right frontal stroke who, despite the ability to draw clocks accurately from memory, translocated numbers on the inferior half of the dial to the superior half when copying a clock. In further graphic and verbal clock reproduction tasks, transpositions were always directed toward the model but disappeared in a delayed copying task. These findings appear to reflect an intentional disorder characterized by pathologic approach behavior.
We tested 125 normal subjects and 24 right and 22 left focal brain-damaged patients (RBD and LBD) on the Rey figure copying test and on a battery of perceptual and representational visuospatial tasks, in search of relationships between constructional and visuospatial abilities. Selected RBD and LBD were not affected by severe aphasia, unilateral spatial neglect or general intellectual defects. Both RBD and LBD showed defective performances on the constructional task with respect to normal subjects. As regards visuospatial tasks, both patient groups scored lower than normal subjects in judging angle width and mentally assembling geometrical figures; moreover, RBD, but not LBD, achieved scores significantly lower than healthy controls in judging line orientation and analyzing geometrical figures. Post-hoc comparisons did not reveal any significant differences between RBD and LBD. Multiple regression analysis showed that visuospatial abilities correlate with accuracy in copying geometrical drawings in normal subjects and in RBD, but not in LBD. From a theoretical perspective, these findings support the idea that visual perceptual and representational abilities do play a role in constructional skills.
We describe a neglect patient who showed systematic transpositions of left-sided items onto the right side in clock drawing. When the patient had to write single hours on blank clock dials he again showed allochiria, while he copied single spatial locations without transpositions. The patient also showed a variable number of spatial transpositions on imaginal tasks with well known and novel material acquired through visual modality and on controlled constructional tasks, independently from response modality (verbal, graphic or motor). From this basis, we argued that spatial transpositions may derive from an impairment of the mental representation of space. Moreover, we speculated that such errors may result from cognitive conflict between different sources of information.
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.