Post by Elisa Guma
What's the science?
As humans, we spend half of our wakeful time attending to our inner world, engaging in thoughts that are unrelated to our external environment. This process, termed internally directed attention, is thought to recruit two distinct functional brain networks: the default network (DN) and the frontoparietal control network (FPCN). The DN is known to activate during internally directed processes (rest, memory retrieval, etc.), whereas the FPCN is known to be involved in control processes. The FPCN can be subdivided into two sub-networks, FPCNA, which is more implicated in internally directed attention, and FPCNB, which is thought to activate during goal-directed behaviours. It is largely unknown how these networks communicate with one another to support internally directed attention. This week in Nature Human Behaviour, Kam and colleagues use intracranial electrophysiological recordings to investigate the connectivity between these two brain networks in the context of internally directed attention.
How did they do it?
The authors recorded intracranial electroencephalogram (EEG) data in 12 individuals with intractable epilepsy who were being monitored to localize seizure onset prior to surgery. Electrodes were categorized to be part of the three networks DN, FPCNA, or FPCNB. Brain activity was recorded while subjects performed a task in which they listened to standard tones (more frequently played), or target tones (less frequently played). They performed the task twice, either with a focus on externally directed attention, in which they were instructed to respond to the target auditory tones, or with an internally directed attention, in which they were instructed to ignore the tones and simply focus on their thoughts. The authors examined differences in brain activity for electrodes within the DN, FPCNA and FPCNB during the two attentional conditions, as well as at different frequency bands of neural activity (theta, alpha, beta).
What did they find?
The authors first ensured that subjects were accurately performing the task by confirming high scores for correct hits and rejections on the externally directed attention portion of the task. Following quality control, the authors were left with 53 DN-FPCNA pairs and 49 DN-FPCNB pairs across subjects. They found that increased signal in a specific frequency band, theta, was observed in the internally directed compared to the externally directed attention condition. Further, they also observed increased connectivity at theta frequency between the DN-FPCNA pairs of electrodes during internally directed attention. In addition, the strength of the theta band connectivity between the two networks was correlated with the attention ratings for internally directed attention, underscoring its role in regulating this type of attention. Conversely, they found a peak in theta band frequency during the externally directed attention between the DN-FPCNB electrodes, highlighting the specificity of the DN-FPCNA connections in guiding internal attention.
What's the impact?
This study found that internally directed attention relies on the interaction between the DN and FPCNA in the theta band frequency recorded using intracranial EEG. These rare intracranial EEG recordings confirm neuroimaging results, and further our understanding of the neural mechanisms underlying internally directed attention. They underscore the value of understanding these specific systems within the context of large-scale brain networks. Clarifying the way in which internal inputs are supported by connectivity between the DN and FPCN could be of interest for future work.
Julia W. Y. Kam et al. Default network and frontoparietal control network theta connectivity supports internal attention. Nature Human Behaviour (2019). Access the original scientific publication here.