, 1981; Mountcastle et al., 1981; Steinmetz et al., 1994; Constantinidis & Steinmetz, 2001b; Ipata et al., 2006). Further, the spatial location coded by the active population of parietal neurons corresponds with the
locus of spatial attention as behaviourally defined, namely as a circumscribed region selleck compound of space where visual processing is enhanced (Powell & Goldberg, 2000; Bisley & Goldberg, 2003). When monkeys are presented with multi-stimulus displays, parietal neurons preferentially encode the location of the most salient stimulus (Gottlieb et al., 1998, 2008b; Kusunoki et al., 2000; Constantinidis & Steinmetz, 2001a, 2005) and have been proposed to provide a ‘priority map’ of visual space (Gottlieb et al., 2008a). Consistent with this is the finding that visual responses of parietal neurons are suppressed to the degree that visual stimuli are effectively ignored (Ipata et al., 2006). The above data indicate that the activity of parietal neurons is correlated with the deployment of attention toward
(or away from) particular check details locations in space. However, it is also possible to direct attention to a specific feature of a visual stimulus (Maunsell & Treue, 2006), irrespective of its spatial position. Interestingly, neurons in the visual motion area MT reflect feature-based attention. Visual signals that are evoked by a motion stimulus presented in the receptive field of MT neurons are stronger if the motion stimulus is moving in the preferred direction of the neuron and the monkey is attending to that direction of motion, even when spatial attention is directed outside of the receptive field (Treue & Martinez Trujillo, 1999). In parietal area 7a, under specific behavioural conditions, visual signals are suppressed if attention is already directed toward the location of a stimulus when the stimulus
appears (Steinmetz et al., 1994; Robinson et al., 1995; Powell & Goldberg, 2000; Constantinidis & Steinmetz, 2001b). This effect has been interpreted to indicate that the activity of area 7a neurons is maximal when stimuli appear that cause spatial attention to move (as in the case that an attention-grabbing stimulus appears outside the current location of attention). The collapse Tideglusib of such a mechanism following parietal damage could explain the difficulty of parietal patients in shifting the locus of spatial attention, which is the essence of what Balint referred to as the ‘psychic paralysis of gaze’. The relative magnitudes of the enhancing and suppressing effects of attention on neural activity in parietal cortex may vary as a function of parietal subdivision and task paradigm; however, both effects substantiate the involvement of PPC in the control of spatial attention at the cellular level.