Getting into the Rhythm of Things: What can our brain signals tell us about mental ill health?
Every time you have to quickly adapt your behaviour after a mistake or in pursuit of a goal, you are using what cognitive scientists and psychologists call cognitive control. It is utilised both when the stakes are high, like when driving through new terrain on a stormy day, and when the stakes are lower, like during a friendly Sunday afternoon game of tennis. Cognitive control allows us to rapidly organise certain behaviours, including perception, planning, decision-making, problem solving, and responsive action to rapidly adapt to and successfully navigate the fast-changing world around us. It allows us to make decisions that best serve long-term interests over immediate rewards and is associated with emotional resilience, both of which are key indicators of mental wellbeing and improved quality of life. Why is it that, despite the existence of this critical ability, we are often vulnerable to irrational influences and can fail to stay focused on our tasks and goals? While our capacity for intelligent goal-directed behaviour is seemingly limitless and the ability to adapt is central to being human, so is making mistakes: to err is human, and we err often. These questions have prompted me and other researchers to attempt to identify precise brain markers of cognitive control that could provide clues as to how we engage strategies to realise our goals and avoid mistakes and why these mechanisms sometimes fail us. I am a Senior Lecturer at King’s College London in the Institute of Psychiatry, Psychology and Neuroscience, who has been working with electroencephalographic (EEG) measures of brain signals — or brain oscillations — in attention deficit/hyperactivity disorder (ADHD), autism, eating disorders and depression.
What are brain oscillations?
The collective behaviour of hundreds of thousands of neurons can be detected from outside the skull using electrodes placed on the scalp. Recording brain signals in this way is referred to as electroencephalography, or EEG. When large groups of neurons transmit electrical signals at the same time, you can observe oscillatory activity in the EEG. Oscillations in the brain occur over a large range of frequencies from very slow 1–4 Hz (or cycles per second) ‘delta’ waves, associated with deep sleep, to higher frequency ‘gamma’ oscillations above 40 Hz that are associated with conscious perception.
EEG acts like a high-speed camera allowing precise measurement of brain activity on a millisecond timescale. This enables the study of rapid changes in the brain that are associated with cognitive control. Even if our environment is often changing and largely unpredictable, accommodation of this unpredictability is built into the operation of our brain.
How does our brain do this?
Brain regions are not continuously active, but rather work in ‘cycles’ of active and inactive periods. This rhythmic, or oscillatory, activity emerges partly due to the interplay between excitatory and inhibitory neurons and allows flexibility in response to the environment as well as predictability.
First come, first served
Much of the research on cognitive control has led us to the frontal lobes of the brain, including the prefrontal cortex (the very front of your brain, the parts right behind your forehead).
For over a century, the brain’s frontal areas have been thought to be the seat of human reason, backed up by many neuroimaging studies. As research in cognitive control has developed, we have been further led to focus on a specific neural activity in this region, namely 4–8 Hz oscillations known as the ‘theta band’, which increase when cognitive control must be utilised and appear to play a key role in the recruitment and organisational timing of function across the brain.
Brain oscillations in the theta band are thought to be fundamentally important for cognitive control in two ways.
First, the predictability of the timing of theta allows the precise co-ordination of activity across brain areas.
Imagine you are playing that game of tennis (or you are Emma Raducanu competing in the US Open!). The fast pace of volleys and return shots necessitates rapid and accurate decision-making. The incoming ball trajectory must be analysed, the return shot prepared, and finally executed at just the right time to strike the ball when and how you intend. The timing of the theta rhythms acts like a precise clock in your brain to predict the optimal time to strike the tennis racket against the ball so that you hit it at just the right speed to get it back across the net.
Second, the relatively fast nature of these oscillations and the precise timing of the active groups of neurons allow for rapid and precise responses in fast changing environments. The timing of these oscillations facilitates the speed of information transfer in the brain so that they act as a gating mechanism for faster processing when necessary. This allows for flexibility and responsiveness in situations of increased conflict or changing demands. Continuing with the above example — when the opposing player sends the ball in an unexpected direction, your theta oscillations will initiate allocation of resources to perception of the ball, planning and action in your body to ensure you move to the optimal location to bat the ball with enough rigor to get it back across the net. Thus, frontal midline theta (like other brain oscillations) enables the balance between predictability and flexibility that is necessary for us to respond advantageously in fast changing environments.
Theta in mental health
As we discover more about how theta responds to challenges or conflicts in our environment, we understand more not only about the optimal function of theta, but also about how and when these oscillations perform suboptimally. In a recent paper in Biological Psychiatry, we set out to understand the role theta rhythms may play in mental ill health. Suboptimally functioning theta can manifest in different ways and take different forms.
Lab studies using cognitive control tasks have shown that in those with anxiety disorders, theta can be imbalanced with an overly large signal strength or amplitude at certain instances, for example overreacting to a mistake. Such a large signal response doesn’t necessarily translate to improved performance and may be related to a weakness in amplitude at other instances, for example when preparing to respond to a stimulus. This has an impact on flexibility of responding so that we may be excessively distracted by unpredictability in our environment, including potential errors, and fail to plan for the next challenge adequately.
We also see dysregulation in the timing of theta in people with disorders such as ADHD. In this case, the onset (or phase) of theta does not act like a precise frequency clock in the brain, which results in responding too quickly or too late to stimuli. As the precise timing of theta is critical for its function as a recruitment mechanism in the brain, dysregulation can have a negative impact on the organisation and overall ‘healthy’ brain function with the result that we do not respond optimally to our environment.
How is this useful?
In 2010, the National Institutes of Health in the United States proposed a new conceptual model to guide research of mental ill health, which focuses on the dimensions of human behaviour and neurobiology rather than on diagnoses based on symptoms. While current diagnostic systems succeed in providing a common clinical language for professionals and allow rough classification of patients for treatment, they can fail to capture the many differences within and across disorders in symptom profiles, causal pathways, and responses to treatment.
Studying the functioning of the nervous system as it relates to critical human processes like cognitive control could help us identify individual issues with cognitive function and flexibility. For example, an individual with low cognitive flexibility, as indicated by irregularities in theta oscillations, could benefit from specific therapeutic treatments that aim to improve the regularity and timing of these rhythms. Initial studies investigating the modification of oscillations in the brain show promising results for a range of disorders, including theta oscillations in schizophrenia and gamma oscillations in Alzheimer’s Disease.
Awareness of these brain dynamics and their role in behaviour is a critical first step towards designing interventions that support individuals’ capacity for healthy and robust cognitive control. This could mean interacting with the environment in a way that allows you to make the best decisions in the moment, to plan ahead and to learn from your mistakes. Life skills that have significance beyond that Sunday afternoon game of tennis.