Anna Sedda

An anatomical account of somatoparaphrenia

Somatoparaphrenia is a delusional belief whereby a patient feels that a paralyzed limb does not belong to his body; the symptom is typically associated with unilateral neglect and most frequently with anosognosia for hemiplegia. This association of symptoms makes anatomical inference based on single case studies not sufficiently specific. On the other hand, the only three anatomical group studies on somatoparaphrenia are contradictory: the right posterior insula, the supramarginal gyrus and the posterior corona radiata, or the right medial or orbito-frontal regions were all proposed as specific lesional correlates. We compared 11 patients with and 11 without somatoparaphrenia matched for the presence and severity of other associated symptoms (neglect, motor deficits and anosognosia). To take into account the frequent association of SP and neglect and hemiplegia, patients with and without somatoparaphrenia were also compared with a group of fifteen right brain damage patients without neglect and hemiplegia. We found a lesion pattern involving a fronto-temporo-parietal network typically associated with spatial neglect, hemiplegia and anosognosia. Somatoparaphrenic patients showed an additional lesion pattern primarily involving white matter and subcortical grey structures (thalamus, basal ganglia and amygdala). Further cortical damage was present in the middle and inferior frontal gyrus, postcentral gyrus and hippocampus. We propose that somatoparaphrenia occurs providing that a distributed cortical lesion pattern is present together with a subcortical lesion load that prevents most sensory input from being processed in neocortical structures; involvement of deep cortical and subcortical grey structures of the temporal lobe may contribute to reduce the sense of familiarity experienced by somatoparaphrenic patients for their paralyzed limb.

Functional magnetic resonance adaptation reveals the involvement of the dorsomedial stream in hand orientation for grasping

Reach-to-grasp actions require coordination of different segments of the upper limbs. Previous studies have examined the neural substrates of arm transport and hand grip components of such actions; however, a third component has been largely neglected: the orientation of the wrist and hand appropriately for the object. Here we used functional magnetic resonance imaging adaptation (fMRA) to investigate human brain areas involved in processing hand orientation during grasping movements. Participants used the dominant right hand to grasp a rod with the four fingers opposing the thumb or to reach and touch the rod with the knuckles without visual feedback. In a control condition, participants passively viewed the rod. Trials in a slow event-related design consisted of two sequential stimuli in which the rod orientation changed (requiring a change in wrist posture while grasping but not reaching or looking) or remained the same. We found reduced activation, that is, adaptation, in superior parieto-occipital cortex (SPOC) when the object was repeatedly grasped with the same orientation. In contrast, there was no adaptation when reaching or looking at an object in the same orientation, suggesting that hand orientation, rather than object orientation, was the critical factor. These results agree with recent neurophysiological research showing that a parieto-occipital area of macaque (V6A) is modulated by hand orientation during reach-to-grasp movements. We suggest that the human dorsomedial stream, like that in the macaque, plays a key role in processing hand orientation in reach-to-grasp movements.

Duckneglect: Video-games based neglect rehabilitation

BACKGROUND Video-games are becoming a common tool to guide patients through rehabilitation because of their power of motivating and engaging their users. Video-games may also be integrated into an infrastructure that allows patients, discharged from the hospital, to continue intensive rehabilitation at home under remote monitoring by the hospital itself, as suggested by the recently funded Rewire project. OBJECTIVE Goal of this work is to describe a novel low cost platform, based on video-games, targeted to neglect rehabilitation. METHODS The patient is guided to explore his neglected hemispace by a set of specifically designed games that ask him to reach targets, with an increasing level of difficulties. Visual and auditory cues helped the patient in the task and are progressively removed. A controlled randomization of scenarios, targets and distractors, a balanced reward system and music played in the background, all contribute to make rehabilitation more attractive, thus enabling intensive prolonged treatment. RESULTS Results from our first patient, who underwent rehabilitation for half an hour, for five days a week for one month, showed on one side a very positive attitude of the patient towards the platform for the whole period, on the other side a significant improvement was obtained. Importantly, this amelioration was confirmed at a follow up evaluation five months after the last rehabilitation session and generalized to everyday life activities. CONCLUSIONS Such a system could well be integrated into a home based rehabilitation system.

Productive symptoms in right brain damage

Purpose of reviewThe purpose of this review is to summarize the more recent studies on productive symptoms from the neuropsychological, neurophysiological and anatomical points of view. The integration of these aspects may provide some clarifications on the cognitive impairments underpinning the main productive disorders, also contributing to better understand the normal functioning of the brain. Recent findingsProductive symptoms are closely associated to spatial neglect and are distinguished in relation to the part of space they manifest. The investigation of perseveration in extrapersonal space with different manipulations helps to understand the neuropathological mechanisms underlying this symptom. Anosognosia for hemiplegia and somatoparaphrenia may be considered as disorders of body representation (personal space). Recently it has been proposed that these disorders may be ascribed to an impairment of different levels of motor control. The identification of the anatomical correlates of these two disorders contributes to better understanding of their the cognitive nature. SummaryProductive behaviours have diverse clinical manifestations and may be induced by different mechanisms. Lesional studies are beginning to provide evidence for specific anatomical correlates of these disorders. Further investigations are needed to better understand to what extent productive symptoms can be disentagled from spatial neglect. These attempts may contribute to clarifying the role of the right hemisphere in monitoring spatial cognition.

Neural correlates of object size and object location during grasping actions

The visuo‐motor channel hypothesis (Jeannerod, 1981) postulates that grasping movements consist of a grip and a transport component differing in their reliance on intrinsic vs. extrinsic object properties (e.g. size vs. location, respectively). While recent neuroimaging studies have revealed separate brain areas implicated in grip and transport components within the parietal lobe, less is known about the neural processing of extrinsic and intrinsic properties of objects for grasping actions. We used functional magnetic resonance imaging adaptation to examine the cortical areas involved in processing object size, object location or both. Participants grasped (using the dominant right hand) or passively viewed sequential pairs of objects that could differ in size, location or both. We hypothesized that if intrinsic and extrinsic object properties are processed separately, as suggested by the visuo‐motor channel hypothesis, we would observe adaptation to object size in areas that code the grip and adaptation to location in areas that code the transport component. On the other hand, if intrinsic and extrinsic object properties are not processed separately, brain areas involved in grasping may show adaptation to both object size and location. We found adaptation to object size for grasping movements in the left anterior intraparietal sulcus (aIPS), in agreement with the idea that object size is processed separately from location. In addition, the left superior parietal occipital sulcus (SPOC), primary somatosensory and motor area (S1/M1), precuneus, dorsal premotor cortex (PMd), and supplementary motor area (SMA) showed non‐additive adaptation to both object size and location. We propose different roles for the aIPS as compared with the SPOC, S1/M1, precuneus, PMd and SMA. In particular, while the aIPS codes intrinsic object properties, which are relevant for hand preshaping and force scaling, area SPOC, S1/M1, precuneus, PMd and SMA code intrinsic as well as extrinsic object properties, both of which are relevant for digit positioning during grasping.

Caloric vestibular stimulation: interaction between somatosensory system and vestibular apparatus

Spatial and bodily representations are multisensory processes that imply the integration of several afferent signals into a coherent internal model of our egocentric space. Crucially, this model involves also the vestibular information from the balance organs in the inner ear (Ventre et al., 1984). Accordingly, vestibular system projections have been proven to overlap with the somatosensory system and with brain regions involved in body and space representation (Bottini et al., 1994, 1995; Fasold et al., 2002). These representations can be altered by a brain lesion and dramatically restored by physiological manipulations targeting specific sensory components, such as the caloric vestibular stimulation (CVS; see for a review Rossetti and Rode, 2002). CVS consists in a water irrigation of the external auditory canal, which induces a change in the temperature that leads to convection currents in the semicircular canals. This evokes a slow-phase nystagmus toward the stimulated ear and it elicits sensations of virtual body rotations and vertigo (Barany, 1906; Silberpfennig, 1941; Barany, 1967). CVS has been used to modulate a wide range of cognitive and sensory functions in brain-damaged patients and in healthy participants (Utz et al., 2011). For instance, in right brain-damaged patients, CVS produces a temporary recovery of visuo-spatial neglect and associated symptoms, such as representational and personal neglect, anosognosia, somatoparaphrenia and motor neglect (see reviews in Rossetti and Rode, 2002; Kerkhoff and Schenk, 2012). Additionally, CVS also influences tactile perception: cold CVS delivered on the left ear transiently reduces tactile imperception (hemianesthesia) in both right and left brain-damaged patients (Vallar et al., 1990, 1993; Bottini et al., 2005). By contrast, the reversed stimulation (i.e., right ear cold CVS) is ineffective in left brain-damaged patients with the interesting exception of left brain-damaged patients with right visuo-spatial neglect (Vallar et al., 1993). More recently, similar cross-modal modulations have been described in healthy participants (Ferre et al., 2010, 2011, 2012, 2013). Various hypotheses have been suggested to explain the CVS-induced modulation on tactile perception. In particular, one of the most controversial issues in the classical and current literature concerns the specificity of these effects. Does CVS directly affect the somatosensory processing? Are the observed effects mediated by non-specific factors, such as ocular movements, spatial attention or general arousal? Since Rubens (1985), most of the scientists believed that positive (e.g., deficits reduction) or negative (e.g., deficits worsening) effects of CVS on spatial deficits in neurological patients can be explained by low-level visuo-vestibular interactions reflecting the direction of the nystagmus (Rubens, 1985). When a leftward nystagmus is present, for instance during left-cold CVS or right-warm CVS, there is a positive effect. Conversely, with a rightward nystagmus (left-warm CVS and right-cold CVS) a deficits worsening is observed (Rubens, 1985; Vallar et al., 1990). However, this traditional explanation has been challenged by several clinical reports which highlighted an effective CVS-induced modulation on deficits that do not require visual control such as personal neglect (Cappa et al., 1987), anosognosia and somatoparaphrenia (Cappa et al., 1987; Bisiach et al., 1991; Rode et al., 1992). Similarly, the remission of hemianesthesia in blind-folded patients (Vallar et al., 1990) rules out this low-level interpretation. Conversely, the role of non-specific effects such as spatial attention is still a matter of debate. This hypothesis argues that CVS may induce a reorientation of spatial attention toward the hemispace ipsilateral to the stimulated ear. Strong evidence against this hypothesis derives from a recent study on brain-damaged patients (Bottini et al., 2005) demonstrating that left-cold CVS also ameliorates right hemianesthesia in left brain-damaged patients (i.e., CVS at same water temperature, same stimulated ear and same leftwards slow-phase nystagmus), independently from the side of stimulation. These behavioral observations have been combined with neuroimaging data to identify the neurofunctional basis of CVS effects on touch perception in a group of normal participants and in one left brain-damaged patient. In this patient, we found that the remission of right hemianesthesia after cold-left CVS was associated with neural activity in the secondary somatosensory cortex (SII) of the undamaged hemisphere. The same region was bilaterally activated in healthy volunteers while they were touched on their right and left hand. Interestingly, the activation of SII for ipsilateral stimuli was of a greater extent in the right than in the left hemisphere in case of left tactile stimulation. These observations have been interpreted as a modulation that did not depend on a lower-level lateral cueing effect, but rather on the activation of the hemisphere that contains a more complete representation of the tactile and body space, the right hemisphere (Bottini et al., 2005). The involvement of SII clearly indicates an overlap between tactile and vestibular projections in the human brain (case RF; Bottini et al., 1995), and it makes explanations in terms of pure spatial effects improbable. More recent behavioral and electrophysiological studies, in healthy participants, have strengthened this suggestion. There are at least three main crucial observations ruling out interpretation in terms of non-specific attentional effects. First, left-cold CVS affects the perception of distinct somatosensory sub-modalities, i.e., touch and pain, for both the ipsilateral and contralateral hand (Ferre et al., 2011, 2013). A simple change in the level of spatial attention would have induced a predominant effect on the hand ipsilateral to the stimulated ear. Second, CVS differentially affects touch and pain. Indeed, while CVS increased sensitivity to tactile stimuli, it reduced levels of pain (Ferre et al., 2013). These further observations cannot be attributed merely to a spatial attention orientation effect, as in this case we would expect the same modulatory effect in both sub-modalities. Finally, CVS enhanced the N80 wave of the somatosensory-evoked potentials (SEPs) elicited by electrical stimulation of tactile afferents (Ferre et al., 2012). Interestingly, the N80 wave is generated in the parietal operculum (Jung et al., 2009; Eickhoff et al., 2010), a region receiving strong vestibular projections. Taken together, clinical observations and psychophysical studies give support to the notion of powerful cross-modal interactions between vestibular and somatosensory systems. Previous studies exploring more widely CVS effects also support the idea that spatial attention does not have a pivotal role. Rorden et al. (2001) did not find an effect of left-cold CVS on covert visual attention in healthy subjects. Furthermore, cold-water bilateral CVS (simultaneous stimulations of the right and left ear) was ineffective on visual neglect in brain-damaged patients, suggesting that CVS might improve neglect through a vestibular-induced specific effect (Rode et al., 2002). Moreover, it has been suggested that CVS can also modify the internal representation of the body (see for an extensive review Lopez et al., 2008). These well documented effects have been explained by the anatomical overlap and interactions of vestibular cortex and somatosensory networks subserving elementary and more structured perceptions concerning the body representation (Lopez et al., 2008, 2012). To conclude, this evidence suggests that in healthy volunteers the effects of CVS are specific and related to the activation of cortico-subcortical networks (Lopez et al., 2012) involved in cross-modal interactions between somatosensory and vestibular signals. We propose that future studies are necessary to extend these findings in neurological patients to better detail the neurophysiological interaction between the somatosensory and the vestibular systems.

In search of the disappeared half of it: 35 years of studies on representational neglect.

OBJECTIVE Representational neglect (RN) is a neuropsychological deficit mostly occurring after right brain damage affecting the mental imagery domain. Patients suffering from RN are unable to represent, describe, or explore the contralesional side of their mental images. Since its first description in 1978, RN has been explored using different theoretical frameworks and experimental paradigms. After 35 years, the nature of its behavioral and anatomical correlates is still unclear. METHOD We reviewed studies on RN published from 1978-2013 to systematize available knowledge and to shed light on future research directions. RESULTS The huge variety of tests used to diagnose RN reflects the different clinical features of the deficit, which can compromise space sectors and memory storage, depending on the stimulus to be imagined, even in a dissociated fashion. RN has been frequently described after parietal, temporal, and frontal right brain lesions, even though reliable group studies are scanty. CONCLUSION A number of priorities concerning RN were identified. Future studies might take into account several aspects of RN that are still poorly explored, starting from a more systematized investigation of RN using larger group studies. RESULTS might add pieces to the puzzle of spatial cognition and its neural basis in mental imagery, paving the way for tailored motor and cognitive rehabilitation programs.

Integration of visual and auditory information for hand actions: preliminary evidence for the contribution of natural sounds to grasping

When we reach out to grasp objects, vision plays a major role in the control of our movements. Nevertheless, other sensory modalities contribute to the fine-tuning of our actions. Even olfaction has been shown to play a role in the scaling of movements directed at objects. Much less is known about how auditory information might be used to program grasping movements. The aim of our study was to investigate how the sound of a target object affects the planning of grasping movements in normal right-handed subjects. We performed an experiment in which auditory information could be used to infer size of targets when the availability of visual information was varied from trial to trial. Classical kinematic parameters (such as grip aperture) were measured to evaluate the influence of auditory information. In addition, an optimal inference modeling was applied to the data. The scaling of grip aperture indicated that the introduction of sound allowed subjects to infer the size of the object when vision was not available. Moreover, auditory information affected grip aperture even when vision was available. Our findings suggest that the differences in the natural impact sounds of objects of different sizes being placed on a surface can be used to plan grasping movements.

Exploring motor and visual imagery in Amyotrophic Lateral Sclerosis

Amyotrophic Lateral Sclerosis (ALS) is a motor neuron disease characterized by the progressive atrophy of both the first and the second motor neurons. Although the cognitive profile of ALS patients has already been defined by the occurrence of language dysfunctions and frontal deficit symptoms, it is less clear whether the degeneration of upper and lower motor neurons affects motor imagery abilities. Here, we directly investigated motor imagery in ALS patients by means of an established task that allows to examine the presence of the effects of the biomechanical constraints. Twenty-three ALS patients and 23 neurologically unimpaired participants have been administered with the (1) hand laterality task (HLT) in which participants were asked to judge the laterality of a rotated hand and the (2) mirror letter discrimination task (MLD) in which participants were asked to judge whether a rotated alphanumeric character was in its canonical or mirror-reversed form (i.e. control task). Results show that patients present the same pattern of performance as unimpaired participants at the MLD, while at the HLT, they present only partially with the effects of biomechanical constraints. Taken together, our findings provide evidences that motor imagery abilities, related to the mental simulation of an action, are affected by this progressive disease.

Body Integrity Identity Disorder: From A Psychological to A Neurological Syndrome

Body Integrity Identity Disorder (BIID) is a condition in which individuals experience an intense desire for amputation of an healthy limb. Recently, McGeoch and colleagues provided the first direct evidence that this syndrome may be neurological rather than psychological in its origin. However, before including BIID in body ownership disorders, several concerns should be clarified, exploring other components of body representation and not only somatosensory perception.