A newly published research in the Vol 16, Issue 4 of Trends in Cognitive Sciences Journal titled “An oscillatory mechanism for prioritizing salient unattended stimuli” proposes an interesting mechanism of prioritizing important impulses employed in the human brain. It does not only offer a fresh point of view on how important synchronized brain-wave activity is for performing complex cognitive tasks, but also can show us the possible organizational structures that could be used to better detect a change in environment and provide fast responses to it.
To provide a short summary: there are several regions inside the brain and each of these regions is “tuned” to a certain frequency. This is how brain regions are functionally separated: a set of neurons is firing in gamma (30-80 Hz) range normally associated with performing cognitive tasks and integrating conscious experience, another set of neurons is firing in the alpha (8 – 12 Hz) range associated with resting active state. These two regions phase-lock and this way “keep track” of each other’s activity.
When a certain unattended impulse becomes sufficiently important, the strength of the alpha-waves increases, leading to a temporary effect on the gamma wave activity and thus bringing the event to the conscious attention. It’s a mechanism that’s used by the brain to indicate that a certain moment is more important than the others and that a certain integrative action is required to deal with it. An example is driving a car and suddenly reacting to a cat running across the road. The houses that are passing by, the pedestrians who are walking alongside the road are all detected by alpha wave activity and their importance is relatively the same in the phase-locked gamma frequency. Once there’s an impulse that is different from the other, the strength of alpha frequency temporarily increases, “informing” the gamma waves about the importance of the event. The driver then decides how to react to this event brought to his consciousness (probably by breaking or changing the direction).
Although this is a simplified description of the main ideas expressed in the paper, it offers and interesting perspective on the way reaction mechanisms work in brain networks. It implies the existence of two sparsely connected networks oscillating at different rhythms, which can come into phase-lock (their oscillations are different, but per 1 iteration in one network there’s approximately 7 oscillations in another). The “slower” rate network is used to detect changes in the environment. An analogy could be a wide range of “informants” within the social network who interact at a certain rate. The “faster” “decision-making” network has a much faster rate of interaction and is used to detect extraordinary events (spikes in activity) in the “informant” network. If the “slower” “informant” network detects an activity worth of attention, it marks it as such in its communication to the “faster” “decision-making” network, which acts as a control center for further action. Within an organization that could be several large networks of “scouts” (seven, for example) and a small, but densely interconnected network of managers. The network of managers has a meeting every day to discuss the current input from each of the “scout” networks. Each of the “scout” networks, in turn, has a meeting once a week at the joint scout-manager meeting to discuss the important events. This organization would allow simultaneous tracking of several different areas of interest and their periodic integration, should the need arise.
It’s also interesting how the relation between gamma and alpha waves is approximately 7 (+- 3), which was shown to be an average number of different things one can be simultaneously conscious about. That is, each iteration of alpha neuron activity requires 7 iterations of gamma neuron activity, so as soon as there are more than 7 sensory inputs they have to start competing for getting a free slot in the gamma frequency and “inform” conscious mind about their presence at the moment when it occurred. Although a speculation, this could be an interesting explanation for the 7 (+- 3) phenomenon.
Photo by CameliatWu@FlickR.