Verbal serial short-term memory and learning have, classically, been attributed to the action of a specialised phonological short-term store localised to the inferior parietal lobe. Recently, however, the behavioural hallmarks of a phonological store have been reinterpreted in terms of articulatory planning and perceptual organisation processes. Two fMRI experiments therefore examined whether patterns of neural activation during verbal serial recall can be explained in terms of articulatory planning processes (instantiated via cortico-cerebellar loops) and modality-specific perceptual processes, without invoking a non-motoric and modality-independent phonological store. It was also examined whether the long-term learning of a verbal sequence is associated with a down-regulation of activity in the cerebellum, consistent with research on motor skill automatisation. Activations associated with articulatory rehearsal of a sequence of letter-names during a retention interval were observed in prefrontal area 9/46, the premotor cortex, and cerebellar lobules HVI and HVIIB—all previously implicated in motor planning—with both auditory (Experiment 1) and visual presentation (Experiment 2). Additionally, activation tied specifically to auditory presentation was observed in the premotor cortex, primary auditory cortex and planum temporale, while activation in the premotor cortex, temporo-occipital-fusiform cortex, intraparietal sulcus, Crus II and lobule HVIIB was observed during visual presentation. Contrary to the phonological store theory, no region in the inferior parietal lobe was found to be active during both stimulus-presentation and rehearsal. Instead, different subdivisions of the intraparietal sulcus were associated with the rehearsal of auditory sequences and with the presentation and rehearsal of visual sequences. Only motor-planning regions were consistently active across both input-modalities and trial-phases, whilst distinct regions were active during presentation as a function of input-modality. While behavioural evidence of sequence learning was observed with both auditory (Experiment 1B) and visual presentation (Experiment 2B), changes in neural activity appeared to reflect general task-set, rather than sequence-specific, learning.
|Award date||1 Nov 2021|
|Publication status||Published - 2021|