Gerardo Salvato

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.

The spatial side of somatoparaphrenia: a case study

Abstract The perception of the bodily self in space is a composite cognitive function requiring a dynamic integrated brain mechanism. Somatoparaphrenia (SP), a delusional belief concerning the experienced disownership for the contralesional paralyzed arm, represents the disruption of such mechanism. In two experiments, we have investigated the alteration of limb disownership after spatial manipulations in a right-brain-damaged patient affected by chronic SP. In experiment 1 the patient’s spatial attention was switched between the left and right sides of space. SP signs worsened when the patient was interviewed from the left compared to the right bedside. In the second experiment we showed the first systematic transient remission of SP using left caloric vestibular stimulation (CVS), a physiologic manipulation mainly acting on the spatial frame of reference. Taken together, these results shed further light on the spatial nuance of SP and on the importance of vestibular signals for the generation of a coherent body representation. Furthermore, our case study demonstrated the possibility of eliciting more severe SP signs if the patient is interviewed from the left bedside. Additionally, CVS applications may have an important impact on the rehabilitation of these symptoms.

Apolipoprotein ɛ4 breaks the association between declarative long-term memory and memory-based orienting of spatial attention in middle-aged individuals

Apolipoprotein (APOE) ɛ4 genotype has been identified as a risk factor for late-onset Alzheimer disease (AD). The memory system is mostly involved in AD, and memory deficits represent its key feature. A growing body of studies has focused on the earlier identification of cognitive dysfunctions in younger and older APOE ɛ4 carriers, but investigation on middle-aged individuals remains rare. Here we sought to investigate if the APOE ɛ4 genotype modulates declarative memory and its influences on perception in the middle of the life span. We tested 60 middle-aged individuals recruited according to their APOE allele variants (ɛ3/ɛ3, ɛ3/ɛ4, ɛ4/ɛ4) on a long-term memory-based orienting of attention task. Results showed that the APOE ɛ4 genotype impaired neither explicit memory nor memory-based orienting of spatial attention. Interestingly, however, we found that the possession of the ɛ4 allele broke the relationship between declarative long-term memory and memory-guided orienting of visuo-spatial attention, suggesting an earlier modulation exerted by pure genetic characteristics on cognition. These findings are discussed in light of possible accelerated brain ageing in middle-aged ɛ4-carriers, and earlier structural changes in the brain occurring at this stage of the lifespan.

Declarative long-term memory and the mesial temporal lobe: Insights from a 5-year postsurgery follow-up study on refractory temporal lobe epilepsy

It is largely recognized that the mesial temporal lobe and its substructure support declarative long-term memory (LTM). So far, different theories have been suggested, and the organization of declarative verbal LTM in the brain is still a matter of debate. In the current study, we retrospectively selected 151 right-handed patients with temporal lobe epilepsy with and without hippocampal sclerosis, with a homogeneous (seizure-free) clinical outcome. We analyzed verbal memory performance within a normalized scores context, by means of prose recall and word paired-associate learning tasks. Patients were tested at presurgical baseline, 6months, 2 and 5years after anteromesial temporal lobe surgery, using parallel versions of the neuropsychological tests. Our main finding revealed a key involvement of the left temporal lobe and, in particular, of the left hippocampus in prose recall rather than word paired-associate task. We also confirmed that shorter duration of epilepsy, younger age, and withdrawal of antiepileptic drugs would predict a better memory outcome. When individual memory performance was taken into account, data showed that females affected by left temporal lobe epilepsy for longer duration were more at risk of presenting a clinically pathologic LTM at 5years after surgery. Taken together, these findings shed new light on verbal declarative memory in the mesial temporal lobe and on the behavioral signature of the functional reorganization after the surgical treatment of temporal lobe epilepsy.

Left caloric vestibular stimulation as a tool to reveal implicit and explicit parameters of body representation

Homeostatic parameters, such as temperature, are related to body representation. In this study, we measured whether caloric vestibular stimulation (CVS) alters body temperature and tactile processing, and if in the direction predicted by a holistic body matrix representation. Skin temperature and tactile two-point discrimination (TPD) acuity were measured for both arms before, immediately after and with a delay from CVS. Participants were also administered a personality questionnaire and an anxiety inventory to rule out confounding factors. Two control experiments were planned to exclude casual variations. Our results show that temperature drops significantly in both arms after CVS. CVS also induces a bilateral improvement in tactile acuity (even though not immediately after but in the delayed condition). Finally, these effects are not due to learning, as demonstrated by the control experiment. In summary, our results suggest that vestibular stimulation updates body representation, supporting the evidence in favor of a body matrix.

“The vestibular system, body temperature and sense of body ownership: a potential link? Insights from a single case study”

The vestibular system plays a pivotal role in behavioural and physiological aspects of body representation. If on the one hand, the stimulation of the vestibular system in healthy subjects provokes body representation distortions, accompanied by a decrease of body temperature, on the other hand, in brain-damaged patients it transiently restores body representation disorders. So far, the physiological counterpart of such behavioural amelioration on patients has never been explored. Here we aimed at investigating body temperature variations following Caloric Vestibular Stimulation (CVS), in a patient affected by somatoparaphrenia who regained the sense of body part ownership after the stimulation. Results showed an increase in body temperature after CVS, which also correlated with the temporary restored sense of limb ownership. Our results support the idea that physiological signals are fundamental to maintain a coherent mental representation of the body.

Multiple Dissociations in Patients with Disorders of Body Awareness: Implications for the Study of Consciousness

Elucidating the nature of consciousness has become one of the most relevant challenges in modern neuroscience. The study of patients with brain damage who exhibit selective impairments in awareness has contributed significantly to redefining the concept of consciousness, shedding light on at least two interesting aspects of its organization: the presence of behavioral and anatomical domain-specific dissociations and the possibility of modulating disturbances in awareness via both central and peripheral stimulations (e.g., caloric vestibular stimulation1—CVS—or transcranial Direct Current Stimulation2—tDCS). Evidence emerging from these lines of research has provided information regarding the nature of conscious processes, their neural substrates, and their associated physiological processes. Anosognosia for hemiplegia (AHP), in which patients with brain damage deny the presence of their contralesional motor deficits (Babinski, 1914), represents how the conscious experience may be finely segmented. Indeed, motor anosognosia can manifest in a limb-specific and modality-specific fashion: For instance, it may affect the upper or lower limbs only (Von Hagen and Ives, 1937; Berti et al., 1996; Moro et al., 2011) and may concern either motor or sensory impairments (i.e., dissociations between AHP and anosognosia for hemianesthesia: AHA; see for exampleMarcel et al., 2004; Spinazzola et al., 2008; Pia et al., 2014). Moreover, previous studies have reported double dissociations between anosognosia and neglect (Bisiach et al., 1986; Berti et al., 1996; Marcel et al., 2004), revealing that AHP does not depend on the attentional deficits typical of Unilateral Spatial Neglect (Bisiach et al., 1986; Berti et al., 1996; Marcel et al., 2004). The existence of these dissociations suggests that brain lesions selectivity affect conscious processes, rather than inducing general and global impairments in awareness. Thus, patients may be aware of one deficit (e.g., hemianesthesia) yet unaware of another (e.g., hemiplegia).

Exploring biased attention towards body-related stimuli and its relationship with body awareness

Stimuli of great social relevance exogenously capture attention. Here we explored the impact of body-related stimuli on endogenous attention. Additionally, we investigate the influence of internal states on biased attention towards this class of stimuli. Participants were presented with a body, face, or chair cue to hold in memory (Memory task) or to merely attend (Priming task) and, subsequently, they were asked to find a circle in an unrelated visual search task. In the valid condition, the circle was flanked by the cue. In the invalid condition, the pre-cued picture re-appeared flanking the distracter. In the neutral condition, the cue item did not re-appear in the search display. We found that although bodies and faces benefited from a general faster visual processing compared to chairs, holding them in memory did not produce any additional advantage on attention compared to when they are merely attended. Furthermore, face cues generated larger orienting effect compared to body and chairs cues in both Memory and Priming task. Importantly, results showed that individual sensitivity to internal bodily responses predicted the magnitude of the memory-based orienting of attention to bodies, shedding new light on the relationship between body awareness and visuo-spatial attention.

Dissociation between preserved body structural description and impaired body image following a pediatric spinal trauma

ABSTRACT In adult patients, Spinal Cord Injury (SCI) may influence the mental Body Representation (BR). Currently, there is no evidence on the modulation of SCI on BR during early stages of cognitive development. Here, we investigated BR in a 3-year-old child with complete SCI. The patient was administered with a specific battery assessing different BR components. We found evidence for putative classical neuropsychological dissociation between a preserved topological map with impaired semantic knowledge of the body. This finding sheds new light on the impact of SCI on BR in childhood, as well as on the level of interdependence between BR’s components..