Massimiliano Conson

Categorical and coordinate spatial processing in the imagery domain investigated by rTMS.

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.

Lateralization of egocentric and allocentric spatial processing after parietal brain lesions

The purpose of this paper was to verify whether left and right parietal brain lesions may selectively impair egocentric and allocentric processing of spatial information in near/far spaces. Two Right-Brain-Damaged (RBD), 2 Left-Brain-Damaged (LBD) patients (not affected by neglect or language disturbances) and eight normal controls were submitted to the Ego-Allo Task requiring distance judgments computed according to egocentric or allocentric frames of reference in near/far spaces. Subjects also completed a general neuropsychological assessment and the following visuospatial tasks: reproduction of the Rey-Osterreith figure, line length judgement, point position identification, mental rotation, mental construction, line length memory, line length inference, Corsi block-tapping task. LBD patients presented difficulties in both egocentric and allocentric processing, whereas RBD patients dropped in egocentric but not in allocentric judgements, and in near but not far space. Further, RBD patients dropped in perceptually comparing linear distances, whereas LBD patients failed in memory for distances. The overall pattern of results suggests that the right hemisphere is specialized in processing metric information according to egocentric frames of reference. The data are interpreted according to a theoretical model that highlights the close link between egocentric processing and perceptual control of action.

Action observation improves motor imagery: specific interactions between simulative processes

In the present study, we demonstrated that observation of hand rotation had specific facilitation effects on a classical motor imagery task, the hand-laterality judgement. In Experiment 1, we found that action observation improved subjects’ performance on the hand laterality but not on the letter rotation task (stimulus specificity). In Experiment 2, we demonstrated that this facilitation was not due to mere observation of a moving hand, because it was triggered by observation of manual rotation but not of manual prehension movements (motion specificity). In Experiment 3, this stimulus- and motion-specific effect was found to be right hand-specific, compatible with left-hemispheric specialization in motor imagery but not in action observation. These data provided direct support to the idea that different simulation states, such as action observation and motor imagery, share some common mechanisms but also show specific functional differences.

Resting state eyes-closed cortical rhythms in patients with locked-in-syndrome: an EEG study

OBJECTIVE Locked-in syndrome (LIS) is a state of complete paralysis, except for ocular movements, which results from ventral brainstem lesions. Patients typically are fully conscious. Here we tested the hypothesis that electroencephalographic (EEG) rhythms are abnormal in LIS patients, possibly due to an impaired neural synchronization between brainstem and cerebral cortex. METHODS Resting state eyes-closed EEG data were recorded in 13 LIS subjects and 15 cognitively normal control subjects. With reference to the individual alpha frequency (IAF), the bands of interest were delta (IAF-8 to IAF-6Hz), theta (IAF-6 to IAF-4Hz), alpha 1 (IAF-4 to IAF-2Hz), alpha 2 (IAF-2 to IAFHz), and alpha 3 (IAF to IAF+2Hz). Furthermore, beta 1 (13-20Hz) and beta 2 (20-30Hz) bands were also considered. Cortical EEG sources were estimated by low-resolution electromagnetic tomography (LORETA). RESULTS The power of alpha 2 and alpha 3 sources in all regions was lower in patients with LIS compared to controls. The power of delta sources in central, parietal, occipital and temporal regions was higher in patients with LIS compared to controls. CONCLUSIONS These results suggest that cortical sources of resting state eyes-closed alpha and delta rhythms are abnormal in LIS patients. SIGNIFICANCE LIS is accompanied by a functional impairment of cortical neuronal synchronization mechanisms in the resting state condition.

A common processing system for duration, order and spatial information: evidence from a time estimation task

The aim of the present study was to verify whether duration, order and space representations share common mechanisms. A two-alternative time estimation paradigm was implemented in two experiments in which subjects had to judge whether the first or the second tone in a pair was shorter (or longer) and to respond by pressing a left or a right key. In Experiment 1, subjects were more accurate in conditions where the first tone was shorter or the second tone was longer, with no effects of spatial information. In Experiment 2, a modification of the paradigm allowed us to demonstrate the presence of a SNARC-like effect, as evidenced by the interaction between order and response key, and of a second-order interaction among duration, order and space. These findings seem consistent with the hypothesis that processing of these three mental categories is subserved by a common mechanism, representing duration and order information according to a spatially-defined magnitude system.

Chapter 19 Visuospatial and visuoconstructive deficits

Publisher Summary This chapter outlines operational definitions of visuospatial and visuoconstructive disturbances. Visuospatial abilities can be intended as those high-order, non-verbal cognitive abilities which operate upon perceptual stimuli and mental images and allow individuals to interact with the environment. The specific inability to construct a complex object, arranging its component elements in their correct spatial relationships is visuoconstructive disturbance. Their clinical and experimental findings regarding visuospatial and constructional disorders and their possible relationships are presented. The most used test to assess visuospatial abilities is the judgment of line orientation test (JLOT), in which subjects are required to identify, among several alternatives, the lines that are at the same orientation as those presented as stimuli. Available cognitive models and some relevant neuroimaging findings aimed at comprehending the mechanisms of constructional disabilities are outlined. Finally, a brief description of several constructional phenomena quite frequent in clinical practice is presented.

Management of pathologic laughter and crying in patients with locked-in syndrome: a report of 4 cases

Emotional lability and pathologic laughter and crying (PLC) have been frequently mentioned in patients with locked-in syndrome (LIS) without giving any detail about the clinical characteristics and possible consequences in terms of symptoms burden, functional impact, and recovery. In the present report, we describe our approach and management of 4 patients with LIS and PLC. PLC caused discomfort to the patients and hindered the different components of their rehabilitation program, limiting communication, the execution of swallowing testing and training, and the improvement of any residual motor function. PLC was unrelated to depression, did not ameliorate after pharmacologic treatment, and improved with cognitive-behavior treatment. Our findings suggest that, in LIS patients, laughter and crying alterations do not represent symptoms of a mood disorder but are the result of the same pontine lesion that causes LIS. In relation to the complex pathway regulating laughter and crying, we hypothesized that, in patients with LIS, PLC may be the result of a direct damage to the pontine center or of an alteration in the ponto-cerebellar pathway linking emotional behavior to contextual information. Presence of PLC in patients with LIS severely affects their intelligent adaptation to the environment. Direct explanation to the patients of the origin of PLC may be helpful as a cognitive-behavior treatment, with resulting benefits to the entire rehabilitation program.

Whose hand is this? Handedness and visual perspective modulate self/other discrimination.

We required healthy subjects to recognize visually presented one’s own or others’ hands in egocentric or allocentric perspective. Both right- and left-handers were faster in recognizing dominant hands in egocentric perspective and others’ non-dominant hand in allocentric perspective. These findings demonstrated that body-specific information contributes to sense of ownership, and that the “peri-dominant-hand space” is the preferred reference frame to distinguish self from not-self body parts.

Movement velocity effects on kinaesthetic localisation of spatial positions

In the present study, we examined how subjects locate spatial positions and code them in short-term memory. In the first experiment, blindfolded subjects were asked to perform movements in the near or far peripersonal space (criterion movement, CM). Then, subjects had to reach the end-point of CM (reproduction movement, RM). Movements could be performed either slowly or rapidly. Also, CM and RM could be performed with the same (congruent conditions) or different velocity (incongruent conditions). The results showed that performance was accurate in the two congruent conditions. Conversely, in the incongruent conditions, subjects made undershoot errors when the CM was fast and overshoot errors when it was slow. In the second experiment, blindfolded subjects also performed CM and RM in congruent or incongruent conditions. However, the CM and RM could start from the same or different position. We found again undershoot errors when the CM was fast and RM was slow and overshoot errors in the reverse condition. The results of both experiments suggest that the information about movement velocity contributes to the kinaesthetic coding in memory of a spatial location to be reached with arm movement.

Brain systems for visual perspective taking and action perception

Taking another persons viewpoint and making sense of their actions are key processes that guide social behavior. Previous neuroimaging investigations have largely studied these processes separately. The current study used functional magnetic resonance imaging to examine how the brain incorporates another persons viewpoint and actions into visual perspective judgments. Participants made a left–right judgment about the location of a target object from their own (egocentric) or an actors visual perspective (altercentric). Actor location varied around a table and the actor was either reaching or not reaching for the target object. Analyses examined brain regions engaged in the egocentric and altercentric tasks, brain regions where response magnitude tracked the orientation of the actor in the scene and brain regions sensitive to the action performed by the actor. The blood oxygen level-dependent (BOLD) response in dorsomedial prefrontal cortex (dmPFC) was sensitive to actor orientation in the altercentric task, whereas the response in right inferior frontal gyrus (IFG) was sensitive to actor orientation in the egocentric task. Thus, dmPFC and right IFG may play distinct but complementary roles in visual perspective taking (VPT). Observation of a reaching actor compared to a non-reaching actor yielded activation in lateral occipitotemporal cortex, regardless of task, showing that these regions are sensitive to body posture independent of social context. By considering how an observed actors location and action influence the neural bases of visual perspective judgments, the current study supports the view that multiple neurocognitive “routes” operate during VPT.