Interhemispheric Transfer of Visual Working Memory

Article: As you look around, mental images bounce between right and left brain
Source: Picower Institute for Learning and Memory at MIT
Published: February 8, 2021

Graphical abstract

When we shift our gaze around to look at a scene, or even temporarily turn away, we rely on visual working memory to retain what we see in mind. The ability to hold that memory enables volitional control of our actions, allowing us to decide to react to something now or later. This visual working memory is a cognitively interesting feat, given that our left visual hemifields correspond to our right cerebral hemisphere, and our right visual hemifields correspond to our left cerebral hemisphere. New research by neuroscientists at MIT, using animal primate models, found that when an object shifts across our field of view, either because it moved or because our eyes did, the brain immediately transfers a memory of it to the opposite (contralateral) brain hemisphere, in particular, to a group of neurons in the prefrontal cortex. Remarkably, even though the new group of neurons encodes the object in the new position, the brain continues to recognize it as the same object that had been in the other hemisphere's field of view. That being said, results in monkeys indicate decreased performance in cases where the monkeys had to shift their gaze, suggesting that shifting gaze requires extra cerebral processing. This switch from one side of one's field of view to the other is accompanied by a signature change in the rhythm of brain wave frequencies to transfer the memory information from one side of the brain to the other. The news article explains, "As the transfer occurred, the synchrony across hemispheres of very low frequency 'theta' waves (~4-10 Hz) and high frequency 'beta' waves (~17-40 Hz) rose and the synchrony of 'alpha/beta' waves (~11-17 Hz) declined." The lead author of the study adds, “This is another form of gating. This time alpha/beta is gating the memory transfer between hemispheres.” Perhaps the most surprising discovery from the experiments was that the prefrontal cortex uses different neurons to encode the memory of an object depending on whether the object (in the same spot of the visual field) was initially seen at that location or transferred there from the other hemisphere. The scientific implication of that finding is the idea that even the same information could still be encoded by different, arbitrarily assembled ensembles of neurons.

My rating of this study: ⭐⭐

Brincat SL, Donoghue JA, Mahnke MK, et al. "Interhemispheric transfer of working memories." Neuron.  8 February 2021. https://doi.org/10.1016/j.neuron.2021.01.016