The results of Buschman et al. (2012) open up a new perspective on the mechanisms of rule use and task switching by positing that rules are implemented by dynamic functional coupling in the PFC network. This suggests several extensions to the cognitive control model proposed by Miller and Cohen (2001). Rule application may
be enabled by a change in dynamic coupling across PFC neurons, leading to selection of task-relevant—and suppression of irrelevant—assemblies. Rule maintenance could be mediated by sustained coherence in the task-relevant assembly. Bias signals might primarily modulate the timing of activity, rather than changing average activity levels in their target neurons, and they would selectively enhance synchrony between relevant sensory, memory, and motor populations. Overall, this updated version of the model fits nicely with previously established SAHA HDAC roles of coupled Rucaparib mouse oscillations for communication and selection (Singer, 1999; Fries, 2005; Engel and Fries, 2010; Siegel et al., 2012). This study is one of few to date that relates research on oscillations and neural coherence to that of higher-level cognitive processes. The data may cast new light on how to implement compositionality (i.e., the ability to form more complex expressions from elementary symbols using syntactic rules) (Reverberi et al.,
2012; Maye and Engel,
2012). A question not addressed in the new study is whether rule processing also involves changes in theta-band (4–8 Hz) or gamma-band (>30 Hz) oscillations, which are both known to occur in PFC and are relevant science for communication of PFC with other brain regions (Womelsdorf et al., 2010; Benchenane et al., 2011). In monkeys, theta-band oscillations in the ACC exhibit rule-specific changes (Womelsdorf et al., 2010). Studies in rodents indicate changes in theta-band coherence between hippocampus and PFC during rule acquisition (Benchenane et al., 2011). Future studies need to clarify the potential role of gamma-band activity for rule use, which in paradigms like binocular rivalry or attention tasks are important for selection of task-relevant assemblies (Singer, 1999; Fries, 2005; Siegel et al., 2012). To establish a complete picture of the role of oscillatory rhythms in rule processing, many aspects of the updated model of cognitive control (Miller and Cohen, 2001) still need to be tested. This includes the exact nature of the bias signals arising from PFC during rule application, as well as the presumed large-scale changes in coherence in the pathways enabled by these bias signals. An important question is whether similar rule selectivity of neural coherence can be observed in other relevant brain structures such as the basal ganglia.