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Developmental biology - Memory Timing
The Brain Uses Two Clocks
To predict the future, memory uses two clocks...
In music and movement, we store memory in two different parts of our brain. One kind of memory for that moment you step on the gas pedal a split second before the light changes, another that moves you to tap your toe upon hearing the first note of a favorite song. This is anticipatory timing. One memory type relies on your past experiences of driving. The other on your stored rhythms. Both are critical to our ability to navigate and enjoy our world.
New University of California, Berkeley, research reveals that two neural networks support each of these time keeping memories in two different parts of our brain, depending on the task.
"Together, these brain systems allow us to not just exist in the moment, but to actively anticipate the future."
Richard B. Ivry PhD, Department of Psychology; Helen Wills Neuroscience Institute, University of California, Berkeley, California USA and study senior author.
"Whether it's sports, music, speech or even allocating attention, our study suggests timing is not a unified process, but are two distinct ways in which we make temporal predictions — and depend on different parts of the brain."
Assaf Breska, postdoctoral researcher, Neuroscience, University of California at Berkeley and study lead author.
Published online in the Proceedings of the National Academy of Sciences (PNAS) journal, these findings offer a new perspective on how humans calculate when to make a move.
Breska and Ivry study anticipatory timing strengths and deficits in people with Parkinson's disease and people with cerebellar degeneration. They connect rhythmic timing to the basal ganglia, and interval timing - to the cerebellum - an internal timer based largely on our memory of prior experiences. Both are primal brain regions associated with movement and cognition. Moreover, their results suggest that if one of these neural clocks is misfiring, the other could theoretically step in.
According to Breska:"Our study identifies not only the anticipatory contexts in which these neurological patients are impaired, but also the contexts in which they have no difficulty. This suggests we could modify their environments to make it easier for them to interact with the world in spite of their symptoms."
Breska believes there is a possibility that non-pharmaceutical 'fixes' for neurological timing deficits might begin with brain-training computer games or perhaps smartphone apps, or deep brain stimulation coupled with environmental design modifications.
Together, he and Ivry compared how well Parkinson's and cerebellar degeneration patients used timing or "temporal" cues to focus their attention on a computer screen. Both groups viewed sequences of red, white and green squares as they flashed by at varying speeds on screen, while encouraged by staff to push a button the moment a green square appeared. White squares preceeded the green square alerting patients the green square was next.
• In one sequence, the red, white and green squares follow a steady rhythm — cerebellar degeneration patients responded well to these rhythmic cues.
• In another, the colored squares followed a more complex pattern, with differing intervals between arrival of the red and green squares. Parkinson's patients performed better on these sequences.
Ivry: "We observed that patients with cerebellar degeneration are impaired in using non-rhythmic temporal cues while patients with basal ganglia degeneration associated with Parkinson's disease are impaired in using rhythmic cues." Ultimately, their results confirm that the brain uses two different mechanisms for anticipatory timing, challenging theories that a single brain system handles all human timing needs.
"Our results suggest at least two different ways in which the brain has evolved to anticipate the future. A rhythm-based system sensitive to periodic events in the world — inherent in speech and music. And an interval system — providing a more general anticipatory ability, sensitive to temporal regularities even in the absence of a rhythmic signal."
Assaf Breska
Significance
The brain uses temporal regularities to anticipate the timing of future events, and adjust attention and action accordingly. We investigated whether subsecond temporal predictions formed in two distinct predictive contexts, when the stream of events is rhythmic or when the specific interval between two events is known, are functionally and neurally distinct. We show that individuals with cerebellar dysfunction were impaired in forming temporal predictions based on single intervals, but not in rhythmic contexts. In contrast, individuals with basal ganglia dysfunction resulting from Parkinson’s disease showed the reverse pattern. This double dissociation constitutes causal evidence in favor of distinct computational and neural mechanisms for interval- and rhythm-based temporal prediction, and highlights the contribution of these subcortical structures to attentional orienting.
Abstract
Predicting the timing of upcoming events is critical for successful interaction in a dynamic world, and is recognized as a key computation for attentional orienting. Temporal predictions can be formed when recent events define a rhythmic structure, as well as in aperiodic streams or even in isolation, when a specified interval is known from previous exposure. However, whether predictions in these two contexts are mediated by a common mechanism, or by distinct, context-dependent mechanisms, is highly controversial. Moreover, although the basal ganglia and cerebellum have been linked to temporal processing, the role of these subcortical structures in temporal orienting of attention is unclear. To address these issues, we tested individuals with cerebellar degeneration or Parkinson’s disease, with the latter serving as a model of basal ganglia dysfunction, on temporal prediction tasks in the subsecond range. The participants performed a visual detection task in which the onset of the target was predictable, based on either a rhythmic stream of stimuli, or a single interval, specified by two events that occurred within an aperiodic stream. Patients with cerebellar degeneration showed no benefit from single-interval cuing but preserved benefit from rhythm cuing, whereas patients with Parkinson’s disease showed no benefit from rhythm cuing but preserved benefit from single-interval cuing. This double dissociation provides causal evidence for functionally nonoverlapping mechanisms of rhythm- and interval-based temporal prediction for attentional orienting, and establishes the separable contributions of the cerebellum and basal ganglia to these functions, suggesting a mechanistic specialization across timing domains.
Authors
Assaf Breska and Richard B. Ivry.
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Dec 4, 2018 Fetal Timeline Maternal Timeline News News Archive
 There are at least two different ways in which the brain anticipates the future. A rhythm-based system sensitive to periodic events inherent in speech and music. And an interval system — sensitive to temporal regularities in the absence of any rhythmic signal. Image Credit: Science Direct.
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