Abstract
ABSTRACT Pain and touch have classically been considered two different sensory modalities. They are implemented by different types of receptors with different densities and receptive fields sizes and characterised by distinct ascending pathways which project in part to different cortical regions. This anatomical segregation is reflected by marked perceptual differences such as the opposite gradients of spatial acuity observed for tactile and nociceptive stimuli. However, recent evidence has suggested a higher degree of integration at the cortical level between the sensory-discriminative aspects of touch and pain. For example, nociceptive somatotopic maps of the digits have been observed in contralateral SI. Crucially, these maps appear highly aligned with those of non-painful tactile stimuli. This possibility raises the question of whether the mechanisms of spatial attention engaged during the processing of tactile and nociceptive stimuli are mediated by distinct or shared neural circuits. Top-down cognitive functions such as spatial attention are known to play a key role in shaping the neural and behavioural responses to painful and tactile stimuli. While recent studies have started to unravel the mechanisms responsible for tactile and nociceptive spatial selectivity, so far these processes have been investigated mostly independently in separate studies. The aim of this project is to compare directly the effects of spatial attention on tactile and nociceptive somatosensory information. Bringing these research fields together and understanding the mechanisms of spatial attention in somatosensation is important not only to broaden our understanding of basic cognitive functions, but also to develop knowledge potentially transferable to clinical practice. Given the close relationship between attention and conscious experience, results of this project will orient the research on the influence of cognitive functioning on pain tolerance. We plan to combine different neuroimaging methods in a convergent manner to gather data with high temporal (i.e., ERPs) and spatial (i.e., fMRI) resolution, exploiting the different expertise present in our teams. We will systematically investigate the neurocognitive mechanisms involved in the control of spatial attention engaged in the anticipation of a forthcoming stimulus when participants receive advance information about its location and modality (tactile vs nociceptive)
Results achieved
Sensory specificity of spatial attention in touch and pain: comparing orienting mechanisms and sensory-specific modulations. The aim of this project was to assess differences and similarities between the neural mechanisms responsible for the orienting and controlling of spatial attention to tactile and nociceptive stimuli and their effects on sensory processing. To this aim we presented an informative cue at the beginning of each trial indicating both the task-relevant modality (touch vs. pain) and the task-relevant location (left or right hand) of a forthcoming target. Participants were then presented with a single target either to the cued or uncued hand, in the cued or uncued sensory modality. Participants’ task was to respond to the target only when presented at the cued location and in the cued modality. This allowed us to address distinct but related questions about attention, by analysing two different sets of data. Cue-elicited brain activity Are similar mechanisms activated during top-down shifts of spatial attention in touch and pain? Brain activity elicited by the cue allowed us to contrast the mechanisms responsible for the orienting of attention towards the relevant body location when participants expect a tactile or a nociceptive stimulus. In the ERP data, we considered the time-course and amplitude of the lateralized ERP components elicited during the cue-target interval. If analogous mechanisms are engaged during shifts of tactile and nociceptive attention, we expected to observe lateralised ERP components similar to those previously observed for touch when the modality cue indicate both pain and touch. Results showed the reliable presence of the ADAN, LDAP and LSN lateralized ERP components in the cue-target interval of both pain-relevant and touch-relevant trials. No timing nor amplitude differences emerged between the lateralized components observed when participants selected pain or touch as task-relevant modalities. These findings suggest the presence of largely overlapping orienting mechanisms involved in spatial attention to touch and to pain. Target-related brain activity Are the effects of spatial attention similar for tactile and nociceptive inputs? The analysis of brain activity elicited by the target as a function of the preceding cue allowed us to directly measure and compare the effects of spatial attention on nociceptive processing (contrasting targets presented at the spatially cued vs uncued location when pain was the cued modality) with those on tactile processing (when touch was cued). Attentional modulations were observed for both touch and pain in the time range of mid-latency (P100, N140) as well as longer latency (Nd1, Nd2) ERP components. Effects of spatial attention on the cued modality were stronger for tactile than painful targets, as shown by larger differences between stimuli delivered to the cued vs uncued hand for touch compared to pain in the Nd1 and Nd2 time windows. The overall reduction of spatial attention effects observed for pain compared to touch was selectively driven by differences between cued ERPs which were less negative for pain than for touch. This observation may indicate differences in spatial selectivity between touch and pain, with reduced attention effects observed for pain indicating a more demanding spatial selection of the cued location when pain was the cued modality. Are there crossmodal links between pain and touch? Typically, when participants attend to the cued location to detect/discriminate stimuli in the cued sensory modality, effects of attention are also observed for stimuli presented at that (cued) location in a different sensory modality (albeit to a smaller extent). Here, we investigated whether and to what extent tactile spatial attention affects the processing of nociceptive stimuli at cued and uncued locations and vice versa (ERP data). Initial behavioural evidence has suggested the presence of crossmodal links from pain to touch, however it remains unknown whether these crossmodal links are bidirectional and the time-course and magnitude of these effects. The comparison between ERPs elicited by stimuli delivered to the cued and uncued hand in the uncued modality mapped systematically the presence and the characteristics of crossmodal links between pain and touch. Results revealed the presence of bidirectional crossmodal links between pain and touch. Directing tactile spatial attention to one hand modulated the N140, Nd1 and Nd2 components elicited by pain stimuli. Likewise, directing spatial attention to one hand to detect pain modulated the N140, Nd1 and Nd2 components elicited by tactile stimuli. These effects were relatively similar for tactile and pain targets, except for the Nd1 time window in which attentional modulations were stronger for touch than for pain. The observation that reduced attentional modulations were present for pain compared to touch regardless of the cued modality (that is when pain was both the cued and uncued modality) suggests that differences between tactile and pain processing may be more related to the specific effects of spatial attention on a given sensory modality, rather than to the attentional mechanis engaged while expecting one or the other modality. Are there differences between the effects of intermodal attention in touch and pain? Intermodal attention is defined as the process of directing attention to one sensory modality as opposed to the other. We contrasted ERPs to tactile targets when touch was the cued vs. the uncued modality (regardless of its spatial location), and ERPs to pain targets when pain was the cued vs. uncued modality. This allowed us to assess whether selecting one sensory modality over the other resulted in selective modulations of brain activity elicited by the target, shedding light on the extent to which the mechanisms responsible for pain and touch selectivity are shared or independent. Results revealed relatively late effects of intermodal attention, with differences between the cued and uncued modality emerging only in the Nd time ranges (200-400ms post stimulus). Notably, effects of intermodal attention emerged earlier for touch than for pain, as revealed by the fact that differences between the cued and uncued modality in the initial Nd time window was observed only for touch. No differences emerged between intermodal attention effects in touch and pain in the Nd2 time window. The late onset of intermodal attention effects and the similar scalp distribution across modalities is consistent with the hypothesis of largely overlapping attentional mechanisms between pain and touch.Dettagli del progetto
Responsabile scientifico: Elena Gherri
Strutture Unibo coinvolte:
Dipartimento di Filosofia
Coordinatore:
ALMA MATER STUDIORUM - Università di Bologna(Italy)
Contributo totale di progetto: Euro (EUR) 204.654,00
Contributo totale Unibo: Euro (EUR) 92.815,00
Durata del progetto in mesi: 28
Data di inizio
18/10/2023
Data di fine:
28/02/2026
