Spatial attention to thermal pain stimuli in subjects with visual spatial hemi-neglect: Extinction, mislocalization and misidentification of stimulus modality

Abstract

One approach to the study of disordered spatial attention is to carry out tests of extinction, in which stimuli are detected on the left when they are presented on the left alone, but not when both sides are stimulated simultaneously in a dual simultaneous stimulation (DSS) protocol. Extinction has been documented for multiple sensory modalities, but not for thermal pain stimuli, to our knowledge. We now test the hypothesis that subjects with visual spatial neglect (hemi-neglect) will have alterations in thermal pain sensation which are related to abnormal spatial attention. The results demonstrate that thermal pain extinction of hot and cold pain stimuli occurs in a proportion of subjects with hemi-neglect. In the subjects with visual spatial hemi-neglect but without thermal pain extinction, the sensation of the thermal pain stimulus on the affected (left) side was not extinguished but was often localized to the unaffected (right) side, and the submodality of the stimulus (cold or hot) was often misidentified. Ratios indicating the magnitude of extinction, mislocalization and misidentification were significantly larger on the left side of subjects with visual spatial neglect than in healthy controls or in controls with stroke but without hemineglect. The proportion of subjects with thermal pain extinction, mislocalization, or misidentification was significantly higher in subjects with hemi-neglect than those in either control group. These results demonstrate that disordered attention exerts a powerful effect upon the perception of both the location and the quality of thermal pain stimuli.

Where is my pain?

“…Complementary to previous descriptions of hemianesthesia after right brain damage [14], Liu et al [11] described two patients with nociceptive extinction. These patients were able to report correctly the occurrence of a nociceptive stimulus when it was applied to their contralesional hand alone.…”

“…For example, it has been shown that covert movement of spatial attention on the body can modify the whole cortical processing of nociceptive stimuli [9]. Even more striking evidence is provided in the present issue of PAIN® by Liu et al [11], who studied detection of nociceptive stimuli in braindamaged patients with a neglect syndrome. Neglect denotes the impaired ability to process or to respond to sensory stimuli presented in the hemiportion of space contralateral to the side of the lesion (most often in the right hemisphere) [4].…”

“…The studies presented here, along with other studies, suggest that nociceptive inputs are integrated in a multimodal system that monitors the section of external space which constitutes a kind of margin of security against potential threats for the body [10]. The studies of Liu et al [11] and Moseley et al [13] open new perspectives in which a comprehensive functional significance of pain is considered: to signal potential physical threats so as to prompt defensive action.…”

“…If we take into account the data from studies that showed a close interaction between nociception and another sensory modality, such as vision [5,12], it can be concluded that the observations made by Liu et al [11] and Moseley et al [13] support the view that the detection and localization of a nociceptive stimulus strongly depends on the attention allocated to the part of the body on which the stimulus is applied, and that the frame of reference which is used to orient attention on the body is a representational frame of reference that depends on the posture of the body (i.e., the position of the limbs relative to each other), the sight of the limbs, and the integration of information from the different senses [10]. This extension of the body in external space, called the peripersonal space (Fig.…”

“…However, the same stimulus was extinguished when it was delivered concomitantly with a nociceptive stimulus delivered to the ipsilesional hand. Liu et al [11] described also seven neglect patients with nociceptive allesthesia: the patients identified correctly the occurrence of a nociceptive stimulus applied to the contralesional hand, but they localized the stimulus as if it had been applied to the ipsilesional hand. These observations demonstrate that in some circumstances the attentional weight that is given to a nociceptive stimulus can be dramatically changed so that its perception becomes completely distorted.…”