Identifying the brain networks that control “off-line” learning

• Research type

  Research Study

• Full title

  Identifying the brain networks that are activated “off-line” following movements using TMS and neuroimaging

• IRAS ID

  181393

• Contact name

  Edwin Robertson

• Contact email

  edwin.robertson@glasgow.ac.uk

• Sponsor organisation

  University of Glasgow

• Duration of Study in the UK

  2 years, 11 months, 30 days

• Research summary

  Research Summary
  Long after playing a game such as football or reading a book, your memory of playing and reading continues to be processed by your brain. These “off-line” processes improve your game and your understanding of the book and more generally, enhance adaptive behaviour, yet we have only a poor understanding of how this happens. Memories can follow different processing routes. For example, some memories are enhanced during periods of wakefulness while with others the enhancement is delayed until sleep. Emerging evidence suggests that inhibitory mechanisms can “switch off” a processing route, preventing the processing of select memories during wakefulness and delaying that processing until sleep. Our project seeks to use a variety of experimental techniques to identify and understand how inhibitory mechanisms operate to prevent memory processing. We will visualise the patterns of brain activation that are specific to inhibiting memory processing and modify them with brain stimulation techniques to alter temporarily the fate of memories. By understanding the mechanisms which control memory processing, we will be able to develop new treatments which exploit those control mechanisms in order to improve rehabilitation in patients with brain injury or stroke

  Summary of Results
  Once formed, the fate of a memory is uncertain. Its fate is sculpted by interactions with other memories even between those for actions (procedural) and events (declarative). Yet, how these interactions occur when different types of memory are predominately processed within segregated systems is poorly understood. A potential bridge across systems are oscillations that co-ordinate activity across networks. These would allow different memory types to be linked to different oscillations within a functional network, and the strength of these oscillations would shape the independence or interaction between memories.
  Networks operate as functional units coupled together by brain oscillations during memory processing. Each of these networks should resist an external perturbation because memory processing is driving them. In much the same way as a child’s swing driven by its own momentum resists the external influence of a parental hand in its continued back-and-forth. In principle, this means that an oscillatory network will become substantially more resistant to perturbation when processing memories. This novel perspective implies the brain activity changes that follow an external perturbation will be substantially reduced by memory processing.
  To test these predictions, we perturbed brain activity following learning using brain stimulation (single pulses of Transcranial Magnetic Stimulation (TMS)) and simultaneously measured its effects upon brain activity (electroencephalography; EEG). Stimulation was applied over brain areas that make key contributions to memory processing (dorsolateral prefrontal cortex, DLPFC; primary motor cortex, M1) at baseline and subsequently “offline”, following memory formation, because this is when processes critical to memory interactions occur.
  Consistent with our hypothesis, we found a reduction in the effect from brain stimulation a within the / band of brain activity during offline memory processing. The DLPFC circuit specifically showed this attenuation when memories interact, whereas the M1 circuit showed it simply due to task performance. This dissociation reveals the central importance of the DLPFC in creating an interaction between memories, which modifies their fate.
  Complementing the anatomical dissociation (DLFPC vs. M1) is a functional dissociation within the DLPFC circuit ( vs.  oscillations). The decreased response within the -band was correlated to impaired procedural skill retention but not declarative word retention. Conversely, the decreased response within the -band was correlated to impaired word but not skill retention. This reveals a novel organization with different memory types being represented by different states ( vs.  oscillations) within a DLPFC circuit, and the power of those states shaping the independence or interaction of one memory type with another.
  Our work shows how segregation between memory systems breaks down. A break down in segregation occurs throughout biology, for example, the separation of ions across membranes breaks down to produce an action potential – here we show another example of this breakdown on a different scale. This is achieved through a novel organization within the prefrontal cortex, in which different memory types are linked to different oscillations, and memory interaction (or independence) shaped by the strength of those oscillations. Overall, this work gives insights into a ubiquitous biological process, the dynamic shift from segregation to interaction, offering new insights into memory organization, and identifies a new relationship between prefrontal physiology and memory content. It achieves this using a novel method to track memory processing

• REC name

  West of Scotland REC 1

• REC reference

  15/WS/0113

• Date of REC Opinion

  26 Jun 2015

• REC opinion

  Further Information Favourable Opinion