Trends in Cognitive Sciences
ReviewThe connectomeNeural correlates of establishing, maintaining, and switching brain states
Section snippets
Brain state
The ability to maintain a brain state (see Glossary) and to switch between states is vital for self-regulation and for adapting to the varying environments that humans occupy. Brain states refer to reliable patterns of brain activity that involve the co-activation and/or connectivity of multiple large-scale brain networks. In infancy, for example, sleep, wakefulness, passive and active alertness, and crying have usually been seen as ranging along a continuum of different levels of arousal [1].
The resting state
Human studies using fMRI have traditionally focused on task-evoked responses. In the past decade, however, the patterns of activity of the human brain during non-task processes (i.e., at rest) have become a focus of several studies 5, 6, 8, 9, 10. In experimental settings, the resting state follows an instruction to lie quietly, relax, and not carry out any task; the eyes may be closed or open, and either fixated or not. Although the resting state does not involve an external task, it shows
The alert state
One important approach to understanding state transitions is to address their relation to slow waves found in electrophysiological recordings. Slow waves, such as the contingent negative variation (CNV), are closely related to aspects of fMRI, since both result from synaptic activity that produces local field potentials 8, 26, 27. The influence of a warning signal on brain activation patterns allows study of the rapid transition to the high levels of alertness needed for rapid and efficient
The meditation state
Unlike the alert state, meditation requires specific training. It is, therefore, difficult to separate the meditation state from the training that produces it. There are many forms of meditation practice, including transcendental meditation, Buddhist meditation, mindfulness meditation, and others 42, 43, 44, 45. Whether the state induced by these various forms of training is the same is not known, so it is difficult to describe a meditation state independent of the training needed to reach it.
Neural correlates of brain state control
Following earlier proposals 76, 77, we hypothesize that the control of brain states includes the two components of switching and maintenance 76, 77. These two components are also present in the transition from rest to alertness and may be general characteristics of state control induced by instruction. The initial response to a warning signal involves an active voluntary response orchestrated by frontal areas including the ACC [30], whereas continued maintenance involves a direct current shift
The alert state and the meditation state
The three brain states are compared in Table 1. The meditation state differs from the alert state induced by a warning signal in several crucial ways. First, the alert state can be induced by the simple instruction to expect a target, without requiring any practice, whereas the meditation state requires specific instruction and practice. Second, the alert state requires an external target, whereas the meditation state may not involve a target event. Third, the alert state involves primarily the
Future directions and applications
In this review, we have examined three brain states: the resting, alert and meditative states. We now consider the significance of understanding these states and suggest directions for future research (Box 2).
Resting state data have been widely applied to the study of normal development 17, 18, 19, 20 and to a variety of neuropsychiatric disorders, including schizophrenia, anxiety, and autism 21, 22. Making use of the ability to image the connectivity of the brain's resting state will continue
Acknowledgements
We would like to thank Rongxiang Tang for assistance with artwork on all figures. This work was supported by 973 Program 2012CB518200, the Office of Naval Research, and NIH grants HD 060563 and R21DA030066 (to Y.Y.T. and M.I.P.).
Glossary
- Alert state
- the brain state that follows a warning related to a target event requiring a rapid response.
- Brain state
- the reliable patterns of brain activity that involve the activation and/or connectivity of multiple large-scale brain networks.
- Contingent Negative Variation (CNV)
- a negative direct current shift in electrophysiological recordings that occurs when a warning signal leads one to prepare for an upcoming target.
- Default Mode Network (DMN)
- a brain network that includes the medial prefrontal
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