PMC:3986539 / 23402-28357 JSONTXT

{"project":"2_test","denotations":[{"id":"24782714-13679398-37408792","span":{"begin":749,"end":753},"obj":"13679398"},{"id":"24782714-20016076-37408793","span":{"begin":773,"end":777},"obj":"20016076"},{"id":"24782714-22875925-37408794","span":{"begin":793,"end":797},"obj":"22875925"},{"id":"24782714-12540901-37408795","span":{"begin":966,"end":970},"obj":"12540901"},{"id":"24782714-16469523-37408796","span":{"begin":984,"end":988},"obj":"16469523"},{"id":"24782714-20303256-37408797","span":{"begin":1007,"end":1011},"obj":"20303256"},{"id":"24782714-24599467-37408798","span":{"begin":1013,"end":1017},"obj":"24599467"},{"id":"24782714-23841841-37408799","span":{"begin":1034,"end":1038},"obj":"23841841"},{"id":"24782714-4023713-37408801","span":{"begin":1852,"end":1856},"obj":"4023713"},{"id":"24782714-10712494-37408802","span":{"begin":1880,"end":1884},"obj":"10712494"},{"id":"24782714-10896165-37408803","span":{"begin":1903,"end":1907},"obj":"10896165"},{"id":"24782714-17610822-37408804","span":{"begin":1926,"end":1930},"obj":"17610822"},{"id":"24782714-23676276-37408807","span":{"begin":3599,"end":3603},"obj":"23676276"},{"id":"24782714-23522051-37408808","span":{"begin":4179,"end":4183},"obj":"23522051"},{"id":"24782714-11850515-37408809","span":{"begin":4358,"end":4362},"obj":"11850515"},{"id":"24782714-2879896-37408810","span":{"begin":4431,"end":4435},"obj":"2879896"},{"id":"24782714-3209731-37408811","span":{"begin":4767,"end":4771},"obj":"3209731"}],"text":"Modulation of visual representations by PFC DA and reward\nAlthough many studies have examined the effect of DA-ergic agents on prefrontal activity, and prefrontal activity has long been believed to modulate responses in visual cortex during attention and working memory, until recently no one had directly examined the effect of locally manipulating prefrontal DA signaling on visual responses in other cortical areas. Noudoost and Moore (2011b) examined the long-range effects of altering prefrontal DA signaling on visual responses in extrastriate area V4. V4, like much of visual cortex, receives direct projections from the Frontal Eye Field (FEF) part of the PFC, an area strongly implicated in controlling spatial attention (Moore and Fallah, 2004; Armstrong et al., 2009; Clark et al., 2012), and it is believed that these projections may be the source of the changes in activity observed in V4 during the deployment of covert attention (Moore and Armstrong, 2003; Awh et al., 2006; Noudoost et al., 2010, 2014; Squire et al., 2013; Clark et al., 2014). Noudoost and Moore examined the effects of manipulating either D1Rs or D2Rs on V4 visual responses during a passive fixation task, and their effect on saccadic target selection in a free-choice task (Noudoost and Moore, 2011a,b). While both D1R and D2R manipulations increased the monkey's tendency to choose the saccade target in the affected region of space, biasing saccadic target selection, only D1Rs had an impact on V4 visual responses. Local injection of a D1R antagonist into the FEF enhanced the strength of visual signals in V4: response magnitude increased, orientation selectivity was enhanced, and trial-to-trial variability decreased (Figure 3). All of these changes are also observed in V4 when covert spatial attention is directed to the V4 neuron's RF (Moran and Desimone, 1985; McAdams and Maunsell, 2000; Reynolds et al., 2000; Mitchell et al., 2007). The reason for the differing effects of FEF D1R and D2R manipulations on V4 activity, but common effects on target selection, may lie in the patterns of receptor expression within the FEF. D1Rs are expressed in both the supragranular layers, which project to V4, and infragranular layers, which contain neurons projecting to motor areas such as the superior colliculus. In contrast, D2Rs are primarily expressed in the infragranular layers. This pattern of expression could account for both receptors influencing target selection, while only D1Rs alter V4 responses (Noudoost and Moore, 2011c).\nFigure 3 The effects of PFC DA on visual cortical activity. Manipulating D1R-mediated FEF activity enhances visual representations in area V4. Noudoost and Moore (2011b) infused a D1R antagonist into the FEF while recording from V4 neurons with RFs either overlapping or not overlapping the area of space represented at the site of drug infusion; the visual responses of the same V4 neurons were recorded before and after infusion of drugs into the FEF. FEF RF center was estimated based on the endpoints of microstimulation-evoked saccades. FEF D1R manipulation caused an increase in orientation selectivity, increase in response magnitude, and decrease in response variability at overlapping V4 sites (orange bars); no effect was seen for non-overlapping V4 sites (green), or saline infusions (gray). These changes in V4 responses with FEF D1R manipulation mimic those seen during covert attention. *p \u003c0.05. Neurophysiological experiments in V1 have provided a direct comparison of the effects of attention and reward on visual cortical responses (Stănişor et al., 2013). Visual responses were shown to be modulated by the relative reward value of the RF stimulus; moreover, the magnitude of this modulation was strongly correlated with the strength of atttentional modulation during a later time window in the same task, and the onset latencies of the two effects were indistinguishable. Like attentional modulation, the neural effects of reward value were dramatically enhanced in the presence of a second stimulus. Human fMRI experiments have also demonstrated a D1R-dependent reward modulation of visual cortical activity (Arsenault et al., 2013). These effects of reward on visual cortex may not be attributable to the PFC—they could result from a bottom-up influence of DA-ergic changes in LGN signaling (Zhao et al., 2002), or via direct DA release from midbrain projections (Lewis et al., 1987). However, several aspects of the findings argue in favor of a prefrontal origin to these effects: the strong correlation with attention in the Stănişor case, the presence of this modulation even in trials without a visual stimulus in the Arsenault paper, the lower density of DA-ergic projections to visual cortex (Berger et al., 1988), and the proven ability of DA-ergic PFC activity to modulate representations in visual cortex (Noudoost and Moore, 2011b), make PFC a likely source of this reward-induced modulation."}