The representation of pleasant touch in the brain and its relationship with taste and olfactory areas

ALTHOUGH there has been much investigation of brain pathways involved in pa in, little is known about the brain mechanisms involved in processing somat osensory stimuli which feel pleasant. Employing fMRI it was shown that plea sant touch to the hand with velvet produced stronger activation of the orbi tofrontal cortex than affectively neutral touch of the hand with wood. In c ontrast, the affectively neutral but more intense touch produced more activ ation of the primary somatosensory cortex than the pleasant stimulus. This indicates that part of the orbitofrontal cortex is concerned with represent ing the positively affective aspects of somatosensory stimuli, and in furth er experiments it was shown that this orbitofrontal area is different from that activated by taste and smell. The finding that three different primary or unlearned types of reinforcer (touch, taste, and smell) are represented in the orbitofrontal cortex helps to provide a firm foundation for underst anding the neural basis of emotions, which can be understood in terms of st ates elicited by stimuli which are rewarding or punishing. (C) 1999 Lippinc ott Williams St Wilkins.