The nature of thought itself?

A fundamental question in neuroscience is how we each form our unique thoughts, memories and perceptions of the world. Ground-breaking work by Earl Miller at MIT, published in Neuron this week, has given some insight into the coding that may lie behind this formation. It appears that neuronal ensembles may be the target if we wish to further unravel the mystery of consciousness.

Researchers used monkeys trained to respond to objects with different colours and orientations; a task selected as it requires decision-making and cognitive flexibility. As the animals performed the task their brainwaves were simultaneously measured, with a focus on the prefrontal cortex, the centre of ‘higher’ thought and processing. Each wave represented an oscillation in neuronal activity in that particular brain region. Different ensembles of neurons are thought to represent different pieces of information.

When the experiment’s monkeys responded to orientation in the task, certain neuronal oscillations attained a high frequency. The result of this is formation of beta-waves. In contrast, upon responding to colour, different groups of neurons produced these waves. Moreover each ensemble had a distinct and recognisable oscillation pattern.

Beta-waves were not the only activity observed. When the ‘colour’ selection task was being performed, neurons in the ‘orientation’ ensemble continued to fire, this time generating low-frequency alpha-waves. It is postulated that these waves have a dampening effect on neuron activity: so in this instance, activity in the ‘orientation’ ensemble could be suppressed by these alpha-waves. Hence this experiment identifies ensembles involved in formation of distinct thoughts and subsequent decisions during a task. Furthermore, the observation of the different characteristic ensemble oscillations implies that consciousness may be inherently rhythmic.

The next step for researchers is to probe the organisation behind the different neuronal ensembles. The coordination between trains of thought ‘flitting’ in and out of our consciousness is “a great mystery” in our understanding of cognition. Some scientists have suggested a role of the thalamus in ensemble coordination, but a great deal of work will be necessary to confirm this.

As Miller explains the basis behind his work: “thoughts (that) float in and out of our heads…are all ensembles forming and reconfiguring…It’s been a mystery how the brain does this.” His research appears to offer a tantalising glimpse into the deepest workings of the mind. Time will tell how far such work will take us in furthering understanding of this elusive branch of neuroscience.