Summary: New research indicates that a failure to switch off the Arc protein promptly after learning may impair cognitive flexibility and the ability to retain new information.
Source: University of Warwick
Researchers identify an essential ‘off‑switch’ for the Arc protein that controls memory, learning and cognitive flexibility
A multinational team co‑led by the University of Warwick has discovered that precise temporal control of the Arc protein is essential for memory formation, learning and cognitive flexibility. This finding improves our understanding of how the brain stores new information and suggests a potential target for tackling memory impairments in neurological diseases such as Alzheimer’s.
Arc (also known as Arg3.1) is an immediate‑early gene product that rises rapidly in neurons during learning and synaptic activity. The new study shows that Arc must be switched off and degraded soon after learning to allow effective memory consolidation and flexible behaviour. If Arc persists longer than it should, the brain’s ability to adapt strategies and incorporate new information is reduced.
Cognitive flexibility is the brain’s capacity to update behaviour and strategies based on new cues—choosing different routes, remembering new locations, or remembering names after a single encounter. This flexibility declines in normal aging and is severely affected in many neurological conditions, including Alzheimer’s disease, producing confusion, repetitive behaviour and difficulty learning and retaining new facts.
The research led by Dr Mark Wall (University of Warwick), Dr Sonia A.L. Corrêa (University of Bradford) and Dr Angela M. Mabb (Georgia State University) demonstrates that the persistence of Arc protein impairs this flexibility. Their experiments show that Arc’s removal by the ubiquitin‑proteasome system acts like an ‘off‑switch’ that limits how long Arc can influence synaptic changes following neuronal activity. When this off‑switch fails, Arc lingers and alters synaptic plasticity in ways that reduce the brain’s ability to switch strategies during reversal learning tasks.
To test the role of Arc’s temporal control, the team engineered mice in which the main ubiquitination sites on Arc were mutated so that the protein was not degraded in the normal timeframe. These Arc knock‑in mice (referred to as ArcKR in the original study) appeared behaviourally normal in many respects and could perform basic spatial learning tasks. However, they showed a clear and selective deficit in reversal learning: when conditions changed and mice needed to adopt a new strategy to solve a task, the mutant animals were impaired.
At the molecular level, the prolonged presence of Arc in these mice lowered the threshold for inducing a form of synaptic depression called mGluR‑LTD and increased its amplitude. This altered synaptic plasticity is consistent with the animals’ reduced ability to change strategies and demonstrates that tightly timed degradation of Arc is crucial for maintaining the flexibility of synaptic signaling needed during learning and memory updating.
Dr Mark Wall explained the behavioural consequence with an analogy: if you move hotel rooms without being told the new location, you might search by trying keys in every door until one opens. Once found, spatial cues make it easy to return quickly. If, however, you had to test every door each time you returned, you would be unable to adapt your approach efficiently. That persistent, inefficient searching mirrors the cognitive inflexibility observed when Arc is not switched off properly.
Dr Sonia A.L. Corrêa added that this kind of inflexibility increases with age and is a characteristic of some neurological disorders, including forms of Alzheimer’s disease. Understanding why the Arc off‑switch malfunctions could point to new therapeutic strategies that restore appropriate temporal control of activity‑dependent proteins and improve learning and memory.
The study was led by Dr Sonia A.L. Corrêa (University of Bradford) and Dr Angela M. Mabb (Georgia State University) in collaboration with Dr Mark Wall (University of Warwick). Additional contributions came from researchers at the University of North Carolina‑Chapel Hill, the University of Utah and Biogen.
Original research — The work was published in Neuron under the title “The Temporal Dynamics of Arc Expression Regulate Cognitive Flexibility” (May 31, 2018). The paper describes how mutation of Arc ubiquitination sites slows its degradation, how Arc knock‑in mice show enhanced mGluR‑LTD, and how persistent Arc reduces cognitive flexibility. DOI: 10.1016/j.neuron.2018.05.012.
Reporting and summary: Luke Walton, University of Warwick. Publisher: NeuroscienceNews.com. Image source: NeuroscienceNews.com (public domain).