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Subjective response and the orbitofrontalSubjective response and the orbitofrontalRepresentation of painful and pleasant in the human orbitofrontal and cingulate cortex E. T. Rolls et al, University of Oxford Cerebral Cortex, 13 (3) pp. 308-17 (2003) doi.10.1093/cercor/13.3.308 http://cercor.oxfordjournals.org/ INTRODUCTION: In this paper, the authors demonstrate that the orbitofrontal and anterior cingulate cortices respond not to the intensity of inputs, but to their emotional positive/negative qualities or else their reward/punisher value as correlated with subjective experience. These brain regions connect to areas important for deciding behaviour, thus demonstrating a connection between subjective response core mechanisms for deciding behaviour. In this study by E.T. Rolls et al, it is demonstrated that some areas of the orbitofrontal cortex are activated more by both pleasant and painful touch than by neutral stimuli. Moreover, the pleasant and painful touches activate different parts of the orbitofrontal. In contrast, the somatosensory cortex was less activated by the pleasant and painful touches than by the neutral stimuli. P. The cingulate cortex is also involved in this study. Part of the anterior cingulate cortex is activated by the pleasant stimulus, and another part of the anterior cingulate is activated by painful stimuli. In contrast, parts of the somatosensory cortex are more activated by the neutral stimuli. The orbitofrontal and to a lesser extent the anterior cingulate cortex are seen here as being adaptive in registering the emotional or reward value aspects of somatosensory stimulation. In an earlier study, the texture of fat in the mouth was demonstrated to activate a population of neurons in the orbitofrontal that is considered likely to indicate the reward value of the food in the mouth. An important study looked at the activation produced by the touch of a piece of velvet and a touch of a piece of wood in the somatosensory cortex, and the activation of the orbitofrontal produced by the same touches. It was demonstrated that the orbitofrontal activation produced by velvet (pleasant) was, relative to the somatosensory activation, proportionately greater than the orbitofrontal activation produced by the neutral touch of wood. A less intense but emotionally or reward value positive stimuli, produced more activation in the orbitofrontal than a more intense but emotionally or reward value neutral stimulus. Similarly an emotionally or reward value negative stimulus also produced more activation in the orbitofrontal than a neutral stimuli that was registered as stronger by the somatosensory cortex. The authors are clear in their conclusion that the orbitofrontal registers emotionally positive or negative aspects of an input, rather than any other aspects such as intensity of signal. Thus their study shows that the external physical force of the velvet was lower than the external physical force of the wood, but the activation in the orbitofrontal was stronger in relation to the velvet than the wood. In addition to this pleasant and painful stimuli activated different parts of the orbitofrontal, whereas a reaction to physical force would presumably not differentiate in the same way. The orbitofrontal is seen by the authors as decoding signals processed by other parts of the brain such as the somatosensory or inferior temporal. Thus the subjective pleasantness of the velvet touch relates directly to the activation level of the orbitofrontal cortex, demonstrating a connection between subjective appreciation and the core mechanisms for decision taking and behaviour. The relationship between the somatosensory and the orbitofrontal is similar to the relationship between the inferior temporal regional and the orbitofrontal when dealing with visual stimuli. The representation in the temporal area is thought to be value neutral, and it acquires its reward/punisher value in the orbitofrontal and other brain regions. P. Anterior cingulate. The anterior cingulate cortex is particularly involved with pain. The anterior cingulate receives adverse projections from the somatosensory, and there is evidence that the emotionally negative quality of inputs is represented in this brain area. Activation in the anterior cingulate was seen to rise and fall in relation to the subjective unpleasantness of stimuli, and not to be related to the in physical intensity of the input signal (Rainville et al, 1999). The cingulate is seen to be indicating the emotionally negative aspects of the signal rather than its physical intensity. Studies showed that single neurons or small numbers of neurons in the cingulate might be responsible for registering these emotional responses. |
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