reticular nucleus, which receives overlapping projections from prefrontal cortex
and higher-order sensory cortical areas, may also play a role in modulating
incoming sensory information with selective attention.”
Daitch et al. (2013) go on to point out that “low-frequency oscillations [of
the alpha type] have been shown to entrain to the rhythm of a task, when
stimuli are presented in a rhythmic, predicable manner. On the other hand,
[gamma] synchrony, which enhances the efficacy of communication between
regions, but which is more metabolically costly than low-frequency activity, may
operate under conditions of temporal uncertainty. Notably, both the pulvinar
and thalamic reticular nucleus, mentioned above as a potential generators of
cortical synchronous activity, operate in both phasic (i.e., transient) and tonic
(i.e., sustained) modes. These two modes may underlie the low frequency versus
sustained high-frequency coherence correlates of attention, respectively.”
As Daitch et al. (2013) note, the oscillations modulated by a task are dete r-
mined by many factors, including the distribution of brain regions recruited,
and so it is not implausible to hypothesize that once we move away from vision,
which is the focus of their study, and appeal to other cortical regions, the very
same mechanisms and rhythms may be at work in generative linguistic cogni-
tion. These regions are plausibly those discussed above in the context of globu-
larity, the default-mode network, and so on: most prominently, the frontal and
parietal association cortices.
Parietal and frontal cortices are indeed key nodes of the working memory
network, and they have been claimed to be modulated by the alpha oscillations
generated by the thalamus during working memory tasks (Roux and Uhlhaas
2014). Roux and Uhlhaas (2014) is in line with Dipoppa and Gutkin (2013).
Both studies seek to ascribe functional meani ng to the various frequencies detected
during specific cognitive tasks. As they write, “although initially thought to reflect
cortical idling, a growing body of evidence critically implicates rhythmic activity
in the alpha band in cortical communication and cognition. Theta activity occurs
preferentially in tasks that involve sequential coding of multiple working memory
items, whereas alpha oscillations tend to occur during tasks that require mainte-
nance of simultaneously presented visual or spatial information.”
Pursuing this idea, Roux and Uhlhaas (2014) note that “modulation of alpha
activity may enab le the gating of task-relevant working memory items, for
example during suppression of distracting information during working memory
encoding and maintenance. In this context, recruitment of alpha-band oscilla-
tions for inhibition of distracting information can also occur during tasks requir-
ing the maintenance of sequential information, highlighting that theta/alpha
frequencies are closely linked to the task demands during working memory and
not limited to the format of working memory representations”. For Roux and
Uhlhaas (2014), “gamma-band oscillations represent a generic me chanism for
the representation of individual working memory items, irrespective of working
memory content and format.”
As Uhlhaas et al. (2010) remark, “alpha activity has been associated not on ly
with inhibitory functions, but also with the long-distance coordination of
242 Constantina Theofanopoulou and Cedric Boeckx