Giuseppe di Pellegrino

Vicarious responses to pain in anterior cingulate cortex: is empathy a multisensory issue?

Results obtained with functional magnetic resonance imaging show that both feeling a moderately painful pinprick stimulus to the fingertips and witnessing another person’s hand undergo similar stimulation are associated with common activity in a pain-related area in the right dorsal anterior cingulate cortex (ACC). Common activity in response to noxious tactile and visual stimulation was restricted to the right inferior Brodmann’s area 24b. These results suggest a shared neural substrate for felt and seen pain for aversive ecological events happening to strangers and in the absence of overt symbolic cues. In contrast to ACC 24b, the primary somatosensory cortex showed significant activations in response to both noxious and innocuous tactile, but not visual, stimuli. The different response patterns in the two areas are consistent with the ACC’s role in coding the motivational-affective dimension of pain, which is associated with the preparation of behavioral responses to aversive events.

Selective deficit in personal moral judgment following damage to ventromedial prefrontal cortex

Recent fMRI evidence has detected increased medial prefrontal activation during contemplation of personal moral dilemmas compared to impersonal ones, which suggests that this cortical region plays a role in personal moral judgment. However, functional imaging results cannot definitively establish that a brain area is necessary for a particular cognitive process. This requires evidence from lesion techniques, such as studies of human patients with focal brain damage. Here, we tested 7 patients with lesions in the ventromedial prefrontal cortex and 12 healthy individuals in personal moral dilemmas, impersonal moral dilemmas and non-moral dilemmas. Compared to normal controls, patients were more willing to judge personal moral violations as acceptable behaviors in personal moral dilemmas, and they did so more quickly. In contrast, their performance in impersonal and non-moral dilemmas was comparable to that of controls. These results indicate that the ventromedial prefrontal cortex is necessary to oppose personal moral violations, possibly by mediating anticipatory, self-focused, emotional reactions that may exert strong influence on moral choice and behavior.

Seeing where your hands are

Some patients with brain damage fail to identify a sensory stimulus presented on the opposite side to their lesion (contralesional) when a competing stimulus is presented on the same side (ipsilesional). This phenomenon has become known as extinction. It is commonly studied using a single sense such as sight or touch (unimodal extinction). We have studied a 75-year-old right-handed man (patient GS) who has severe left tactile extinction resulting from damage to the right frontotemporal cortex caused by a stroke. We found that an ipsilesional visual stimulus could induce extinction of a contralesional tactile stimulus (cross-modal extinction). We also found that the visual stimulus operates in a reference system attached to the hand, and not in egocentric coordinates (that is retinal, head or trunk-centred coordinates).

Sex differences in eye gaze and symbolic cueing of attention

Observing a face with averted eyes results in a reflexive shift of attention to the gazed-at location. Here we present results that show that this effect is weaker in males than in females (Experiment 1). This result is predicted by the ‘extreme male brain’ theory of autism (Baron-Cohen, 2003), which suggests that males in the normal population should display more autism-like traits than females (e.g., poor joint attention). Indeed, participants′ scores on the Autism-Spectrum Quotient (Baron-Cohen, Wheelwright, Stott, Bolton, & Goodyear, 2001) negatively correlated with cueing magnitude. Furthermore, exogenous orienting did not differ between the sexes in two peripheral cueing experiments (Experiments 2a and 2b). However, a final experiment showed that using non-predictive arrows instead of eyes as a central cue also revealed a large gender difference. This demonstrates that reduced orienting from central cues in males generalizes beyond gaze cues. These results show that while peripheral cueing is equivalent in the male and female brains, the attention systems of the two sexes treat noninformative symbolic cues very differently.

Neuropsychological Evidence of an Integrated Visuotactile Representation of Peripersonal Space in Humans

Current interpretations of extinction suggest that the disorder is due to an unbalanced competition between ipsilesional and contralesional representations of space. The question addressed in this study is whether the competition between left and right representations of space in one sensory modality (i.e., touch) can be reduced or exacerbated by the activation of an intact spatial representation in a different modality that is functionally linked to the damaged representation (i.e., vision). This hypothesis was tested in 10 right-hemisphere lesioned patients who suffered from reliable tactile extinction. We found that a visual stimulus presented near the patients ipsilesional hand (i.e., visual peripersonal space) inhibited the processing of a tactile stimulus delivered on the contralesional hand (cross-modal visuotactile extinction) to the same extent as did an ipsilesional tactile stimulation (unimodal tactile extinction). It was also found that a visual stimulus presented near the contralesional hand improved the detection of a tactile stimulus applied to the same hand. In striking contrast, less modulatory effects of vision on touch perception were observed when a visual stimulus was presented far from the space immediately around the patients hand (i.e., extrapersonal space). This study clearly demonstrates the existence of a visual peripersonal space centered on the hand in humans and its modulatory effects on tactile perception. These findings are explained by referring to the activity of bimodal neurons in premotor and parietal cortex of macaque, which have tactile receptive fields on the hand and corresponding visual receptive fields in the space immediately adjacent to the tactile fields.

The Regulation of Cognitive Control following Rostral Anterior Cingulate Cortex Lesion in Humans

The contribution of the medial prefrontal cortex, particularly the anterior cingulate cortex (ACC), to cognitive control remains controversial. Here, we examined whether the rostral ACC is necessary for reactive adjustments in cognitive control following the occurrence of response conflict [Botvinick, M. M., Braver, T. S., Barch, D. M., Carter, C. S., & Cohen, J. D. Conflict monitoring and cognitive control. Psychological Review, 108, 624652, 2001]. To this end, we assessed 8 patients with focal lesions involving the rostral sector of the ACC (rACC patients), 6 patients with lesions outside the frontal cortex (non-FC patients), and 11 healthy subjects on a variant of the Simon task in which levels of conflict were manipulated on a trial-by-trial basis. More specifically, we compared Simon effects (i.e., the difference in performance between congruent and incongruent trials) on trials that were preceded by high-conflict (i.e., incongruent) trials with those on trials that were preceded by low-conflict (i.e., congruent) trials. Normal controls and non-FC patients showed a reduction of the Simon effect when the preceding trial was incongruent, suggestive of an increase in cognitive control in response to the occurrence of response conflict. In contrast, rACC patients attained comparable Simon effects following congruent and incongruent events, indicating a failure to modulate their performance depending on the conflict level generated by the preceding trial. Furthermore, damage to the rostral ACC impaired the posterror slowing, a further behavioral phenomenon indicating reactive adjustments in cognitive control. These results provide insights into the functional organization of the medial prefrontal cortex in humans and its role in the dynamic regulation of cognitive control.

Social modulation of peripersonal space boundaries.

The space around the body, i.e., peripersonal space (PPS), is conceived as a multisensory-motor interface between body and environment. PPS is represented by frontoparietal neurons integrating tactile, visual, and auditory stimuli occurring near the body. PPS is plastic, because it extends by using a tool to reach far objects. Although interactions with others occur within PPS, little is known about how social environment modulates it. Here, we show that presence and interaction with others shape PPS representation. Participants performed a tactile detection task on their face while concurrent task-irrelevant sounds approached toward or receded from their face. Because a sound affects touch when occurring within PPS, we calculated the critical distance where sounds speeded up tactile reaction time as a proxy of PPS boundaries. Experiment 1 shows that PPS boundaries shrink when subjects face another individual, as compared to a mannequin, placed in far space. Experiment 2 and 3 show that, after playing an economic game with another person, PPS boundaries between self and other merge, but only if the other behaved cooperatively. These results reveal that PPS representation is sensitive to social modulation, showing a link between low-level sensorimotor processing and high-level social cognition.

Spatial extinction on double asynchronous stimulation

Despite the fact that visual extinction is widely considered a space-based disturbance of selective attention, there has been little theoretical consensus about the nature of its pathogenic mechanism. A specific disruption in the ability to disengage attention from ipsilesional stimuli, or a loss of weight with which contralesional objects compete for visual selection, have been hypothesized to account for the disorder. We tested the merits of these two explanations in a right-hemisphere-lesioned patient, FB, who failed to recognize a contralesional target only when it was shown concurrently to an ipsilesional target (i.e. visual extinction). His task was to report two target letters presented in rapid succession to the left and right of the fixation point. The order of stimulus presentation (Left-First vs Right-First), and the intertarget interval (stimulus onset asynchrony) were varied systematically. We showed that contralesional extinction may occur for successively presented targets, not just for stimuli displayed at the same time. Of most importance, FB was seriously and equally impaired in dealing with a contralesional stimulus when this either preceded the ipsilesional stimulus or followed it by an interval less than about 600 msec. The data appear to contradict the disengagement hypothesis, which predicted a substantial reduction of extinction when a stimulus was displayed first into the lesioned side of space. We suggest that a competitive model of visual selective attention fits the data quite well.

Seeing or not seeing where your hands are

Abstract. Previous findings have demonstrated the existence of a visual peripersonal space centered on the hand in humans and its modulatory effects on tactile perception. A strong modulatory effect of vision on touch perception was found when a visual stimulus was presented near the hand. In contrast, when the visual stimulus was presented far from the hand, only a weak modulatory effect was found. The aim of the present study was to verify whether such cross-modal links between touch and vision in the peripersonal space centered on the hand could be mediated by proprioceptive signals specifying the current hand positions or if they directly reflect an interaction between two sensory modalities, i.e., vision and touch. To this aim, cross-modal effects were studied in two different experiments: one in which patients could see their hands and one in which vision of their hands was prevented. The results showed strong modulatory effects of vision on touch perception when the visual stimulus was presented near the seen hand and only mild effects when the vision of the hand was prevented. These findings are explained by referring to the activity of bimodal neurons in premotor and parietal cortex of macaque, which have tactile receptive fields on the hand, and corresponding visual receptive fields in the space immediately adjacent to the tactile fields. One important feature of these bimodal neurons is that their responsiveness to visual stimuli delivered near the body part is reduced or even extinguished when the view of the body part is prevented. This implies that, at least for the hand, the vision of the hand is crucial for determining the spatial mapping between vision and touch that takes place in the peripersonal space. In contrast, the proprioceptive signals specifying the current hand position in space do not seem to be relevant in determining the cross-modal interaction between vision and touch.

Direct evidence from parietal extinction of enhancement of visual attention near a visible hand

Brain areas exist that appear to be specialized for the coding of visual space surrounding the body (peripersonal space). In marked contrast to neurons in earlier visual areas, cells have been reported in parietal and frontal lobes that effectively respond only when visual stimuli are located in spatial proximity to a particular body part (for example, face, arm or hand) [1-4]. Despite several single-cell studies, the representation of near visual space has scarcely been investigated in humans. Here we focus on the neuropsychological phenomenon of visual extinction following unilateral brain damage. Patients with this disorder may respond well to a single stimulus in either visual field; however, when two stimuli are presented concurrently, the contralesional stimulus is disregarded or poorly identified. Extinction is commonly thought to reflect a pathological bias in selective vision favoring the ipsilesional side under competitive conditions, as a result of the unilateral brain lesion [5-7]. We examined a parietally damaged patient (D.P.) to determine whether visual extinction is modulated by the position of the hands in peripersonal space. We measured the severity of visual extinction in a task which held constant visual and spatial information about stimuli, while varying the distance between hands and stimuli. We found that selection in the affected visual field was remarkably more efficient when visual events were presented in the space near the contralesional finger than far from it. However, the amelioration of extinction dissolved when hands were covered from view, implying that the effect of hand position was not mediated purely through proprioception. These findings illustrate the importance of the spatial relationship between hand position and object location for the internal construction of visual peripersonal space in humans.