Primate color in V4, motion direction in

Primate
brain is highly capable to integrate the information of multiple sensory areas
together to perceive environment uniquely. In a particular sensory system, this
integration of features known as “feature binding”. In the visual system, various
visual features of an object thought to be dominantly processed in the separate areas of the brain. For instance, color in V4, motion
direction in MT, shape in V1 and V2 etc. The main question of visual
feature binding is how the brain integrates these features of an object
together and separates them from other objects.

Two main
theories related to feature binding are “binding by synchrony” (BBS) and
“feature integration theory” (FIT). The BBS theory proposed that feature
binding is performed by the synchronous activity of the involving neurons (Von
der Malsburg, 1994, Elliott& Müller, 1998, Gray and Singer, 1989). However,
it is limited to this fact that how two components of the same dimension could
be bounded (grouping), rather than two features from different dimensions (Shadlen
& Movshon, 1999 Thiele & Stoner, 2003, Palanca & DeAngelis, 2005, Ray,
2010, Martin, Anne, 2015). In FIT theory the perception of an object is
completed in two stages, feature separation, and feature combination (Treisman
and Gelade, 1980). This theory suggests the attention as the main component in
feature integration mechanism (Treisman and Gelade, 1980, Treisman &
Schmidt 1982, Schoenfeld 2003, Cohen. 2013, Katzner 2006,  Golomb, L’Heureux, & Kanwisher, 2014, Robertson,
2003). A number of studies reported some forms of feature conjunction in absent
of attention (Houck 1986, Gajewski, 2006, Mordkoff, 2008) or similar function
of attention in working memory (Allen, Hitch, & Baddeley, 2009; Brown &
Brockmole, 2010; Fougnie & Marois, 2009). The feature binding has been
reported in several areas of the brain; from early visual areas (Seymour et al,
2009) to parietal cortex (Friedman, 1995, Shafritz, 2002). However, the exact
neural mechanism of it is yet unknown. In addition, since most of these studies
were based on functional imaging and psychophysics, a lack of neural evidence
of this mechanism is observed.

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A clue
to resolve the binding problem is the hierarchical process and the probability
of  governing the feature conjunction by
a high-level area of the brain. It is widely believed that cortex encodes
visual stimuli in a hierarchical manner (Riesenhuber
and Poggio, 1999). The prefrontal
cortex which is placed on the top of this hierarchy and houses the inputs from
both ventral and dorsal visual streams is an ideal region for this purpose (SFuster,
1988). In addition, single neurons of this area encode the direction, color, position
and behaviorally relevance visual features (Rainer
et al., 1998; Ninokura et al., 2004, Miller
and Cohen, 2001; Rigotti et al., 2013). Furthermore, it had been revealed that there
is a task-specific top-down information transmission from prefrontal cortex to
early visual areas (Yosuke Morishima 2009).

To
examine the role of PFC in feature binding, using an electrophysiological study
we investigated the existence of feature conjunction in the prefrontal cortex. Results
indicate that the integration of color and motion direction features, which are
dominantly appearance in the areas v4 and MT respectively, encodes in the prefrontal
cortex. Furthermore, it was shown that this coding arrises in the low-frequency
theta and alpha of LFP signal. We further, found that the feature binding is
emerged in the single sites of PFC neurons and also propagated into surrounding
neurons. Finally, we showed that this binding information is behaviorally
relevant.

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