Impulse responses reveal unimodal and bimodal access to visual and auditory working memory

Abstract

It is unclear to what extent sensory processing areas are involved in the maintenance of sensory information in working memory (WM). Previous studies have thus far relied on finding neural activity in the corresponding sensory cortices, neglecting potential activitysilent mechanisms such as connectivity-dependent encoding. It has recently been found that visual stimulation during visual WM maintenance reveals WM-dependent changes through a bottom-up neural response. Here, we test whether this impulse response is uniquely visual and sensory-specific. Human participants (both sexes) completed visual and auditory WM tasks while electroencephalography was recorded. During the maintenance period, the WM network was perturbed serially with fixed and task-neutral auditory and visual stimuli. We show that a neutral auditory impulse-stimulus presented during the maintenance of a pure tone resulted in a WM-dependent neural response, providing evidence for the auditory counterpart to the visual WM findings reported previously. Interestingly, visual stimulation also resulted in an auditory WM-dependent impulse response, implicating the visual cortex in the maintenance of auditory information, either directly, or indirectly as a pathway to the neural auditory WM representations elsewhere. In contrast, during visual WM maintenance only the impulse response to visual stimulation was content-specific, suggesting that visual information is maintained in a sensory-specific neural network, separated from auditory processing areas. Significance StatementWorking memory is a crucial component of intelligent, adaptive behaviour. Our understanding of the neural mechanisms that support it has recently shifted: rather than being dependent on an unbroken chain of neural activity, working memory may rely on transient changes in neuronal connectivity, which can be maintained efficiently in activity-silent brain states. Previous work using a visual impulse stimulus to perturb the memory network has implicated such silent states in the retention of line orientations in visual working memory. Here, we show that auditory working memory similarly retains auditory information. We also observed a sensory-specific impulse response in visual working memory, while auditory memory responded bi-modally to both visual and auditory impulses, possibly reflecting visual dominance of working memory.

Decoding visual colour from scalp electroencephalography measurements

“…To increase sensitivity and to ease visualisation, we reduced these tuning-profiles from Fig. 2 B, to a single decodability value per time point, by convolving the tuning profiles with a cosine function ( van Ede, Chekroud, Stokes, and Nobre, 2018 ; Wolff et al., 2019 ; as in Wolff et al., 2017 ). Decoding time-courses are depicted in Fig.…”

Temporally distinct oscillatory codes of retention and manipulation of verbal working memory

“…However, the figures show that decoding accuracy quickly deteriorated and even approached the chance level towards the end of the delay (<1 s). In another study employing the same approach the accuracy of the classification declined below chance level shortly before the end of the delay, i.e., 700 ms after the delay onset (Wolff et al, 2019). The fact that it was possible to decode only the attended item, led to a conclusion that neural activity may represent not the entire content but only information in the focus of attention (Lewis-Peacock et al, 2011; Stokes, 2015; Wolff et al, 2015, 2017).…”

Pinging reveals active, not silent, working memories

“…While absent decoding should not be taken as direct evidence for activity-silent storage [29], the opposite is true: being able to decode is evidence for active storage. Evidence for EEG code reactivations [7,24,[30][31][32][33] remain fundamental in showing the remarkable effects of visual pinging, in particular for exploring how it interacts with actively held [20,24], not activity-silent, memories.…”