Competitive state of actions during planning predicts sequence execution accuracy

SummaryHumans can learn and retrieve novel skilled movement sequences from memory, yet the content and structure of sequence planning are not well understood. Previous computational and neurophysiological work suggests that actions in a sequence are planned as parallel graded activations and selected for output through competition (competitive queuing; CQ). However, the relevance of CQ during planning to sequence fluency and accuracy, as opposed to sequence timing, is unclear. To resolve this question, we assessed the competitive state of constituent actions behaviourally during sequence preparation. In three separate multi-session experiments, 55 healthy participants were trained to retrieve and produce 4-finger sequences with particular timing from long-term memory. In addition to sequence production, we evaluated reaction time (RT) and error rate increase to constituent action probes at several points during the preparation period. Our results demonstrate that longer preparation time produces a steeper CQ activation and selection gradient between adjacent sequence elements, whilst no effect was found for sequence speed or temporal structure. Further, participants with a steeper CQ gradient tended to produce correct sequences faster and with a higher temporal accuracy. In a computational model, we hypothesize that the CQ gradient during planning is driven by the width of acquired positional tuning of each sequential item, independently of timing. Our results suggest that competitive activation during sequence planning is established gradually during sequence planning and predicts sequence fluency and accuracy, rather than the speed or temporal structure of the motor sequence.HighlightsPre-ordering of actions during sequence planning can be assessed behaviourallyCompetitive gradient reflects sequence preparedness and skill, but not speed or timingGradient is retrieved rapidly and revealed during automatic action selectionPositional tuning of actions boosts the competitive gradient during planning

Neural competitive queuing of ordinal structure underlies skilled sequential action

The fluent retrieval and production of movement sequences is essential for a variety of daily activities such as speech, tool-use, musical and athletic performance, but the neural mechanisms underlying sequence planning remain elusive. Here, participants learned sequences of finger presses with different timings and different finger orders, and reproduced them in a magneto-encephalography (MEG) scanner. We classified the MEG patterns immediately preceding each press in the sequence, and examined their dynamics over the production of the whole sequence. Our results confirm a role for the ‘competitive queuing’ of upcoming action representations in the production of learned motor sequences, extending previous computational and non-human primate recording studies to non-invasive measures in humans. In addition, we show that competitive queuing does not simply reflect specific motor actions, but representations of higher-level sequential order that generalise across different motor sequences. Finally, we show that the quality of competitive queuing predicts participants’ production accuracy, and originates from parahippocampal and cerebellar sources. These results suggest that the brain learns and produces multiple behavioural sequences by flexibly combining representations of specific actions with more abstract, parallel representations of sequential structure.

Memory for Serial Order in Alzheimer’s Disease and Vascular Dementia: A Competitive Queuing Analysis

Objective Competitive Queuing (CQ) models of memory for serial order comprise two layers: parallel planning where target items are activated and competitive choice where serial order is specified. The application of CQ models regarding healthy and pathological aging has received little attention. Method Participants included patients with Alzheimer’s disease (AD; n = 26), vascular dementia (VaD; n = 29), and healthy controls (HC; n = 35). Memory for serial order in the visual domain was assessed using the Object Span Task, where participants briefly viewed then drew a sequence of four figures. Percent correct and total errors (omissions, intrusions, repetitions, transpositions) were computed for each serial position. Results Significant primacy effects were detected in each group. AD and VaD participants were less accurate and showed more omission and between-trial repetition errors than HC (HC < AD = VaD, p < .05). VaD participants produced more transposition and intrusion errors than the AD and HC groups (HC < AD < VaD, p < .05). A group × position interaction was significant for omissions (p < .05), with AD and VaD participants producing more omissions in later serial positions (SP1 < SP2 < SP3 < SP4, all p values < .05). Conclusions Analysis of accuracy and errors by serial position identified unique patterns of performance across groups that suggest involvement of distinct layers of response activation and selection. Serial order difficulties in AD may be due to weakened activation of task items affecting later serial positions, whereas poor performance in VaD may be due to weakened activation plus interference from extraneous stimuli at all serial positions.