Visually induced central pain and arm withdrawal after right parietal lobe infarction

In search of conditioned pain: an experimental analysis

ABSTRACT

There is an ongoing debate about whether pain can be classically conditioned, but surprisingly, evidence is scarce. Here, we report 3 experiments investigating this idea. In a virtual reality task, healthy participants were approached and touched near or on their hand with a coloured pen (blue or yellow). During acquisition, participants learned that one of the colours of the pen (CS+) was predictive of a painful electrocutaneous stimulus (ECS) whereas the other coloured pen (CS-) was not. During the test phase, more frequent reports of experiencing an US when none was delivered ("false alarm") for the CS+ vs CS- qualified as evidence of conditioned pain. Notable differences between experiments were that the US was delivered when the pen touched a spot between the thumb and index finger (experiment 1; n = 23), when it virtually touched the hand (experiment 2; n = 28) and when participants were informed that the pen caused pain rather than simply predicting something (experiment 3; n = 21). The conditioning procedure proved successful in all 3 experiments: Self-reported fear, attention, pain, fear, and US expectancy were higher ( P < 0.0005) for the CS+ than the CS-. There was no evidence for conditioned pain in experiment 1, but there was some evidence in experiments 2 and 3. Our findings indicate that conditioned pain may exist, albeit most likely in rare cases or under specific situations. More research is needed to understand the specific conditions under which conditioned pain exists and the underlying processes (eg, response bias).

[A role of cognitive and emotional factors in formation of pain]

Pain is influenced by multiple emotional and cognitive factors. This paper provides an overview of the most important emotional and cognitive factors affecting pain, which has been confirmed in experimental and clinical studies. Emotional factors that increase pain perception include anxiety, depression, and other negative emotions. Positive emotions lead to a decrease in pain. Cognitive factors such as attention, expectation anxiety, and pain assessment can both increase and decrease pain sensations, depending on their specific focus. It becomes clear that pain is not just a reflection of nociceptive irritation, but also a feeling formed by psychological factors that can be individual in each case.

Where am I? Who am I? The Relation Between Spatial Cognition, Social Cognition and Individual Differences in the Built Environment

Knowing who we are, and where we are, are two fundamental aspects of our physical and mental experience. Although the domains of spatial and social cognition are often studied independently, a few recent areas of scholarship have explored the interactions of place and self. This fits in with increasing evidence for embodied theories of cognition, where mental processes are grounded in action and perception. Who we are might be integrated with where we are, and impact how we move through space. Individuals vary in personality, navigational strategies, and numerous cognitive and social competencies. Here we review the relation between social and spatial spheres of existence in the realms of philosophical considerations, neural and psychological representations, and evolutionary context, and how we might use the built environment to suit who we are, or how it creates who we are. In particular we investigate how two spatial reference frames, egocentric and allocentric, might transcend into the social realm. We then speculate on how environments may interact with spatial cognition. Finally, we suggest how a framework encompassing spatial and social cognition might be taken in consideration by architects and urban planners.

Neural correlates of an illusory touch experience investigated with fMRI

When asked to judge the presence or absence of near-threshold tactile stimuli, participants often report touch experiences when no tactile stimulation has been delivered ('false alarms'). The simultaneous presentation of a light flash during the stimulation period can increase the frequency of touch reports, both when touch is and is not present. Using fMRI, we investigated the BOLD response during both light-present and light-absent false alarms, testing predictions concerning two possible neural mechanisms underlying these illusory touch experiences: activation of a tactile representation in primary somatosensory cortex (SI) and/or activation of a tactile representation in late processing areas outside of sensory-specific cortex, such as medial prefrontal cortex (MPC). Our behavioural results showed that participants made false alarms in light-present and light-absent trials, both of which activated regions of the medial parietal and medial prefrontal cortex including precuneus, posterior cingulate and paracingulate cortex, suggesting the same underlying mechanism. However, only a non-significant increase in SI activity was measured in response to false alarm vs. correct rejection trials. We argue that our results provide evidence for the role of top-down regions in somatic misperception, consistent with findings from studies in humans and non-human primates.

Dipole source analyses of laser evoked potentials obtained from subdural grid recordings from primary somatic sensory cortex

The cortical potentials evoked by cutaneous application of a laser stimulus (laser evoked potentials, LEP) often include potentials in the primary somatic sensory cortex (S1), which may be located within the subdivisions of S1 including Brodmann areas 3A, 3B, 1, and 2. The precise location of the LEP generator may clarify the pattern of activation of human S1 by painful stimuli. We now test the hypothesis that the generators of the LEP are located in human Brodmann area 1 or 3A within S1. Local field potential (LFP) source analysis of the LEP was obtained from subdural grids over sensorimotor cortex in two patients undergoing epilepsy surgery. The relationship of LEP dipoles was compared with dipoles for somatic sensory potentials evoked by median nerve stimulation (SEP) and recorded in area 3B (see Baumgärtner U, Vogel H, Ohara S, Treede RD, Lenz FA. J Neurophysiol 104: 3029-3041, 2010). Both patients had an early radial dipole in S1. The LEP dipole was located medial, anterior, and deep to the SEP dipole, which suggests a nociceptive dipole in area 3A. One patient had a later tangential dipole with positivity posterior, which is opposite to the orientation of the SEP dipole in area 3B. The reversal of orientations between modalities is consistent with the cortical surface negative orientation resulting from superficial termination of thalamocortical neurons that receive inputs from the spinothalamic tract. Therefore, the present results suggest that the LEP may result in a radial dipole consistent with a generator in area 3A and a putative later tangential generator in area 3B.

Beyond the window: multisensory representation of peripersonal space across a transparent barrier

A large body of neuropsychological evidence has been recently provided showing that humans can code visual objects in nearby space through multisensory visuo-tactile integrative processes, which share several similarities with the functional properties of bimodal neurons documented in neurophysiological studies. In particular, the phenomenon of visuo-tactile extinction reveals that crossmodal integration may take place in a privileged manner within a limited sector of space closely surrounding the body surface, i.e. in the near peripersonal space. Here we report that visuo-tactile extinction can seemingly be obtained when a physical, transparent barrier is interposed between the patients' hand and a proximal visual stimulus. These findings show that visuo-tactile representation of peripersonal space can be formed despite the subject's explicit awareness concerning the physical impossibility for the hand to be touched. This phenomenon indicates that multisensory integrative processing can occur in a bottom-up fashion without necessarily being modulated by more 'cognitive' processes. Such integration may be functionally important for automatic reactions such as head turning or hand withdrawal.

Central representation of chronic ongoing neuropathic pain studied by positron emission tomography

This study was undertaken to explore whether the neural substrates demonstrated in brain imaging studies on experimentally induced pain are involved in the perception of chronic neuropathic pain. We investigated the cerebral representation of chronic lateralised ongoing pain in patients with painful mononeuropathy (PMN, i.e., pain in the distribution of a nerve, neuralgia) with positron emission tomography (PET), using regional cerebral blood flow (rCBF) as an index for neuronal activity. Eight patients (29-53 years) with PMN in the lower extremity (4 in the right, 4 in the left) were recruited. Paired comparisons of rCBF were made between the patient's habitual pain (HP) state and the pain alleviated (PA) state following a successful regional nerve block (RNB) with lidocaine. The ongoing neuropathic pain resulted in activation of bilateral anterior insula, posterior parietal, lateral inferior prefrontal, and posterior cingulate cortices as well as the posterior sector of the right anterior cingulate cortex (ACC), Brodmann area (BA) 24, regardless of the side of PMN. In addition, a reduction in rCBF was noted in the contralateral posterior thalamus. No significant change of rCBF was detected in the somatosensory areas, i.e., SI and SII. The cerebral activation pattern, while addressing the differences between the HP and PA states, emphasises the affective-motivational dimension in chronic ongoing neuropathic pain. The striking preferential activation of the right ACC (BA 24), regardless of the side of the PMN, not only confirms that the ACC participates in the sensorial/affectional aspect of the pain experience but also suggests a possible right hemispheric lateralisation of the ACC for affective processing in chronic ongoing neuropathic pain. Our data suggests that the brain employs different central mechanisms for chronic neuropathic pain and experimentally induced acute pain, respectively.