Abstract
The world around us is replete with stimuli that unfold over time. When we hear an auditory stream like music or speech or scan a texture with our fingertip, physical features in the stimulus are concatenated in a particular order. This temporal patterning is critical to interpreting the stimulus. To explore the capacity of mice and humans to learn tactile sequences, we developed a task in which subjects had to recognise a continuous modulated noise sequence delivered to whiskers or fingertips, defined by its temporal patterning over hundreds of milliseconds. GO and NO-GO sequences differed only in that the order of their constituent noise modulation segments was temporally scrambled. Both mice and humans efficiently learned tactile sequences. Mouse sequence recognition depended on detecting transitions in noise amplitude; animals could base their decision on the earliest information available. Humans appeared to use additional cues, including the duration of noise modulation segments.
Highlights
To make sense of the world around us, the brain must integrate sensory patterns and sequences over time and assign them meaning
Mice were trained to distinguish between initially meaningless GO and NO-GO sequences built from series of identical ‘syllables’, with the sequences differing only in that syllables were scrambled in time over hundreds of milliseconds
Mice tested with an identical stimulus paradigm achieved similar recognition of a sequence delivered to their whiskers, but appeared to base their performance primarily on detecting the presence of particular relative changes in noise amplitude. Senses such as touch or hearing depend critically on the detection of temporal patterning over timescales from tens of milliseconds to seconds: in these sensory modalities, signals unfold over time and Figure 6 continued envelope. (B) Binary sequences distinguishable based on syllable ordering or the durations of small-amplitude epochs
Summary
To make sense of the world around us, the brain must integrate sensory patterns and sequences over time and assign them meaning. Fast sensory events, such as fluctuations in the forces acting on a whisker follicle, are encoded faithfully and with high temporal precision (Johnson, 2001; Johansson and Birznieks, 2004; Jones et al, 2004; Chagas et al, 2013; Bale et al, 2015; Campagner et al, 2016; Bush et al, 2016). Exploring an object by scanning with fingertips or whiskers generates a series of tactile events concatenated over time (Phillips and Johnson, 1985; Phillips et al, 1990; Weber et al, 2013; Maravall and Diamond, 2014; Sofroniew and Svoboda, 2015; Saal et al, 2016). Recognising the object as a whole – its texture, shape or size – requires integrating over these events, with the relevant timescales varying from tens of milliseconds (ms) to seconds
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