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Several computational models make predictions about the activation states of individual elements of an action sequence during planning and execution; however, the neural mechanisms of action planning are still poorly understood. Simple chaining models predict that only the first response in an action sequence should be active during planning. Conversely, some parallel activation models suggest that during planning, a serial inhibition process places the individual elements of the action into a serial order across a winner-takes-all competitive choice gradient in which earlier responses are more active, and hence likely to be selected for execution compared with later responses. We triggered transcranial magnetic stimulation pulses at 200 or 400 ms after the onset of a five-letter word, in which all but one response was planned and typed with the left hand, except for a single letter which required a right index finger response exclusively at one of five serial positions. We measured the resulting motor-evoked potentials at the right index finger as a marker for the activation state of that planned response. We observed no difference in motor-evoked potential amplitude across any serial position when a right index finger response was planned at 200 ms after the onset of the word; however, we observed a graded pattern of activation at 400 ms, with earlier positions that required a right index finger response showing greater motor-evoked potentials amplitude compared with later positions. These findings provide empirical support for competitive queuing computational models of action planning. [ABSTRACT FROM AUTHOR]

A central model that describes how behavioral sequences are produced features a neural architecture that readies different movements simultaneously, and a mechanism where prioritized suppression between the movements determines their sequential performance. We previously described a model whereby suppression drives a Drosophila grooming sequence that is induced by simultaneous activation of different sensory pathways that each elicit a distinct movement (Seeds et al., 2014). Here, we confirm this model using transgenic expression to identify and optogenetically activate sensory neurons that elicit specific grooming movements. Simultaneous activation of different sensory pathways elicits a grooming sequence that resembles the naturally induced sequence. Moreover, the sequence proceeds after the sensory excitation is terminated, indicating that a persistent trace of this excitation induces the next grooming movement once the previous one is performed. This reveals a mechanism whereby parallel sensory inputs can be integrated and stored to elicit a delayed and sequential grooming response.

Motor sequences are formed through the serial execution of different movements, but how nervous systems implement this process remains largely unknown. We determined the organizational principles governing how dirty fruit flies groom their bodies with sequential movements. Using genetically targeted activation of neural subsets, we drove distinct motor programs that clean individual body parts. This enabled competition experiments revealing that the motor programs are organized into a suppression hierarchy; motor programs that occur first suppress those that occur later. Cleaning one body part reduces the sensory drive to its motor program, which relieves suppression of the next movement, allowing the grooming sequence to progress down the hierarchy. A model featuring independently evoked cleaning movements activated in parallel, but selected serially through hierarchical suppression, was successful in reproducing the grooming sequence. This provides the first example of an innate motor sequence implemented by the prevailing model for generating human action sequences.

Humans can learn and produce skilled movement sequences from memory, yet the nature of sequence planning is not well understood. Previous computational and neurophysiological work suggests that movements in a sequence are planned as parallel graded activations and selected for output through competition. However, the relevance of this planning pattern to sequence production fluency and accuracy, as opposed to the temporal structure of sequences, is unclear. To resolve this question, we assessed the relative availability of constituent movements behaviorally during the preparation of motor sequences from memory. In three separate multisession experiments, healthy participants were trained to retrieve and produce four-element finger press sequences with particular timing according to an abstract sequence cue. We evaluated reaction time (RT) and error rate as markers of movement availability to constituent movement probes. Our results demonstrate that longer preparation time produces more pronounced differences in availability between adjacent sequence elements, whereas no effect was found for sequence speed or temporal grouping. Further, participants with larger position-dependent differences in movement availability tended to initiate correct sequences faster and with a higher temporal accuracy. Our results suggest that competitive preactivation is established gradually during sequence planning and predicts sequence skill, rather than the temporal structure of the motor sequence. NEW & NOTEWORTHY Sequence planning is an integral part of motor sequence control. Here, we demonstrate that the competitive state of sequential movements during sequence planning can be read out behaviorally through movement probes. We show that position-dependent differences in movement availability during planning reflect sequence preparedness and skill but not the timing of the planned sequence. Behavioral access to the preparatory state of movements may serve as a marker of sequence planning capacity. [ABSTRACT FROM AUTHOR]

Many complex actions are mentally pre-composed as plans that specify orderings of simpler actions. To be executed accurately, planned orderings must become active in working memory, and then enacted one-by-one until the sequence is complete. Examples include writing, typing, and speaking. In cases where the planned complex action is musical in nature (e.g. a choreographed dance or a piano melody), it appears to be possible to deploy two learned sequences at the same time, one composed from actions and a second composed from the time intervals between actions. Despite this added complexity, humans readily learn and perform rhythm-based action sequences. Notably, people can learn action sequences and rhythmic sequences separately, and then combine them with little trouble (Ullén & Bengtsson 2003). Related functional MRI data suggest that there are distinct neural regions responsible for the two different sequence types (Bengtsson et al. 2004). Although research on musical rhythm is extensive, few computational models exist to extend and inform our understanding of its neural bases. To that end, this article introduces the TAMSIN (Timing And Motor System Integration Network) model, a systems-level neural network model capable of performing arbitrary item sequences in accord with any rhythmic pattern that can be represented as a sequence of integer multiples of a base interval. In TAMSIN, two Competitive Queuing (CQ) modules operate in parallel. One represents and controls item order (the ORD module) and the second represents and controls the sequence of inter-onset-intervals (IOIs) that define a rhythmic pattern (RHY module). Further circuitry helps these modules coordinate their signal processing to enable performative output consistent with a desired beat and tempo. [ABSTRACT FROM AUTHOR]

Calligraphic writing presents many challenges for motor control, including: learning and recall of stroke sequences; critical timing of stroke onsets and durations; fine control of grip and contact forces; and letterform invariance under size scaling, which entails fine control of stroke directions and amplitudes during recruitment and derecruitment of musculoskeletal degrees of freedom. Experimental and computational studies in behavioral neuroscience have progressed toward explaining the learning, planning, and control exercised in tasks that share features with calligraphic writing and drawing. This article highlights component operations ranging from parallel sequence representations to fine force control. Treated in succession are: competitive queuing models of sequence representation, performance, learning, and recall; letter size scaling and motor equivalence; cursive handwriting models in which sensory-motor transformations are performed by circuits that learn inverse differential kinematic mappings; and fine-grained control of timing and transient forces by circuit models that learn to solve inverse dynamics problems. [ABSTRACT FROM AUTHOR]

A central model that describes how behavioral sequences are produced features a neural architecture that readies different movements simultaneously, and a mechanism where prioritized suppression between the movements determines their sequential performance. We previously described a model whereby suppression drives a Drosophila grooming sequence that is induced by simultaneous activation of different sensory pathways that each elicit a distinct movement (Seeds et al., 2014). Here, we confirm this model using transgenic expression to identify and optogenetically activate sensory neurons that elicit specific grooming movements. Simultaneous activation of different sensory pathways elicits a grooming sequence that resembles the naturally induced sequence. Moreover, the sequence proceeds after the sensory excitation is terminated, indicating that a persistent trace of this excitation induces the next grooming movement once the previous one is performed. This reveals a mechanism whereby parallel sensory inputs can be integrated and stored to elicit a delayed and sequential grooming response.

We present a novel model, SCP1, of monkey sequence learning that takes the processes of stimulus recognition and motor planning seriously in addressing a robust dataset on list learning obtained through the Simultaneous Chaining Paradigm (SCP). Strikingly, SCP violates stimulus-response (S-R) mappings in that after several different lists are learned, monkeys are able to conserve this learning on a new list which is “conserved” in the sense that the jth element is specified as the jth element of any one of the previously learned lists. We demonstrate list acquisition as a result of multiple concurrent learning processes that together contribute to competent performance. In addition to reproducing behavioral results, we offer observations linking the work to macaque neurophysiology. [ABSTRACT FROM AUTHOR]

Understanding the logic behind how a fruit fly's brain tells it to groom its body parts in a stereotyped order might help us understand other behaviours that also involve a series of actions.

Motor sequences are formed through the serial execution of different movements, but how nervous systems implement this process remains largely unknown. We determined the organizational principles governing how dirty fruit flies groom their bodies with sequential movements. Using genetically targeted activation of neural subsets, we drove distinct motor programs that clean individual body parts. This enabled competition experiments revealing that the motor programs are organized into a suppression hierarchy; motor programs that occur first suppress those that occur later. Cleaning one body part reduces the sensory drive to its motor program, which relieves suppression of the next movement, allowing the grooming sequence to progress down the hierarchy. A model featuring independently evoked cleaning movements activated in parallel, but selected serially through hierarchical suppression, was successful in reproducing the grooming sequence. This provides the first example of an innate motor sequence implemented by the prevailing model for generating human action sequences.

In this paper, we describe a case of nonlinear spelling and its implications for theories of the graphemic buffer. C.T.J., an individual with an acquired deficit of the graphemic buffer, often wrote the letters of his responses in a nonlinear temporal order when writing to dictation. The spatial ordering of the letters was maintained: Letters in the later positions of the words were written towards the right side of the response, even when written before letters in earlier positions. This unusual phenomenon has been briefly reported in three prior cases but this study provides the most detailed analysis of the phenomenon to date. We specifically contend that the decoupling of the temporal and spatial aspects of spelling is difficult to reconcile with competitive queuing accounts of the graphemic buffer. [ABSTRACT FROM AUTHOR]

How is the serial order of a spatial sequence represented in short-term memory (STM)? Previous research by Farrell and Lewandowsky (Farrell & Lewandowsky, 2004; Lewandowsky & Farrell, 2008) has shown that 5 alternative mechanisms for the representation of serial order can be distinguished on the basis of their predictions concerning the response times accompanying transposition errors. We report 3 experiments involving the output-timed serial recall of sequences of seen spatial locations that tested these predictions. The results of all 3 experiments revealed that transposition latencies are a negative function of transposition displacement, but with a reduction in the slope of the function for postponement, compared with anticipation errors. This empirical pattern is consistent with that observed in serial recall of verbal sequences reported by Farrell and Lewandowsky (2004), and with the predictions of a competitive queuing mechanism, within which serial order is represented via a primacy gradient of activations over items combined with associations between items and positional markers, and with suppression of items following recall. The results provide the first clear evidence that spatial and verbal STM rely on some common mechanisms and principles for the representation of serial order. [ABSTRACT FROM AUTHOR]

From vocabulary learning to imitating sequences of motor actions, the ability to plan, represent, and recall a novel sequence of items in the correct order is fundamental for many verbal and nonverbal higher level cognitive activities. Here we review phenomena of serial order documented across the verbal, visual, and spatial short-term memory domains and interpret them with reference to the principles of serial order and ancillary assumptions instantiated in contemporary computational theories of memory for serial order. We propose that functional similarities across domains buttress the notion that verbal, visual, and spatial sequences are planned and controlled by a competitive queuing (CQ) mechanism in which items are simultaneously active in parallel and the strongest item is chosen for output. Within the verbal short-term memory CQ system, evidence suggests that serial order is represented via a primacy gradient, position marking, response suppression, and cumulative matching. Evidence further indicates that output interference operates during recall and that item similarity effects manifest during both serial order encoding and retrieval. By contrast, the principles underlying the representation of serial order in the visual and spatial CQ systems are unclear, largely because the relevant studies have yet to be performed. In the spatial domain, there is some evidence for a primacy gradient and position marking, whereas in the visual domain there is no direct evidence for either of the principles of serial order. We conclude by proposing some directions for future research designed to bridge this and other theoretical gaps in the literature. [ABSTRACT FROM AUTHOR]

A mirror system is active both when an animal executes a class of actions (self-actions) and when it sees another execute an action of that class. Much attention has been given to the possible roles of mirror systems in responding to the actions of others but there has been little attention paid to their role in self-actions. In the companion article (Bonaiuto et al. Biol Cybern 96:9–38, 2007) we presented MNS2, an extension of the Mirror Neuron System model of the monkey mirror system trained to recognize the external appearance of its own actions as a basis for recognizing the actions of other animals when they perform similar actions. Here we further extend the study of the mirror system by introducing the novel hypotheses that a mirror system may additionally help in monitoring the success of a self-action and may also be activated by recognition of one’s own apparent actions as well as efference copy from one’s intended actions. The framework for this computational demonstration is a model of action sequencing, called augmented competitive queuing, in which action choice is based on the desirability of executable actions. We show how this “what did I just do?” function of mirror neurons can contribute to the learning of both executability and desirability which in certain cases supports rapid reorganization of motor programs in the face of disruptions. [ABSTRACT FROM AUTHOR]

How does the brain carry out working memory storage, categorization, and voluntary performance of event sequences? The LIST PARSE neural model proposes an answer that unifies the explanation of cognitive, neurophysiological, and anatomical data. It quantitatively simulates human cognitive data about immediate serial recall and free recall, and monkey neurophysiological data from the prefrontal cortex obtained during sequential sensory-motor imitation and planned performance. The model clarifies why spatial and non-spatial working memories share the same type of circuit design. It proposes how laminar circuits of lateral prefrontal cortex carry out working memory storage of event sequences within layers 6 and 4, how these event sequences are unitized through learning into list chunks within layer 2/3, and how these stored sequences can be recalled at variable rates that are under volitional control by the basal ganglia. These laminar prefrontal circuits are variations of visual cortical circuits that explained data about how the brain sees. These examples from visual and prefrontal cortex illustrate how laminar neocortex can represent both spatial and temporal information; and open the way towards understanding how other behaviors derive from shared laminar neocortical designs. [ABSTRACT FROM AUTHOR]

Sequential behavior is observed in various domains of cognitive psychology, including free recall paradigms. In this article, within a neurocomputational framework, resampling (RS) mechanisms are compared with competitive queuing (CQ) mechanisms. While both types of implementations select the most active representation, the subsequent inhibition is at the level of selection for RS models and at the level of (re)activation for CQ models. It is shown that despite the overwhelming success of CQ models in serial recall (with regard to types of sequencing error) RS models outperform CQ models with regard to inter-response times in a free recall task. Additional analyses show that decay of response suppression reduces the difference between the models. The RS model is sensitive to the size of the search set and accounts for memory selection performance in patients with Alzheimer's dementia or Huntington's disease. Finally, a non-mnemonic clustering behavior is observed, which is related to the dynamical process of the selection mechanism. [ABSTRACT FROM AUTHOR]

In this paper we examine the role of stored semantic knowledge in recall from short-term memory. We assessed the performance of a patient (FK), who showed a consistent lack of semantic knowledge for some words (‘unknown’) but not others (‘known’) on a range of serial recall tasks using both spoken and written words. Overall, FK was significantly better at recalling lists of known compared with unknown words. His recall of unknown words was characterized by numerous phonological errors, such as repeating ‘bear skunk’ as ‘bunk scare’. FK showed a relatively normal primacy effect in immediate recall, but a striking lack of a recency effect. This pattern of performance is useful for constraining theoretical accounts of language production and verbal short-term memory and for understanding the role that long-term semantic knowledge may play in maintaining information in short-term memory. [ABSTRACT FROM AUTHOR]

A central model that describes how behavioral sequences are produced features a neural architecture that readies different movements simultaneously, and a mechanism where prioritized suppression between the movements determines their sequential performance. We previously described a model whereby suppression drives a Drosophila grooming sequence that is induced by simultaneous activation of different sensory pathways that each elicit a distinct movement (Seeds et al., 2014). Here, we confirm this model using transgenic expression to identify and optogenetically activate sensory neurons that elicit specific grooming movements. Simultaneous activation of different sensory pathways elicits a grooming sequence that resembles the naturally induced sequence. Moreover, the sequence proceeds after the sensory excitation is terminated, indicating that a persistent trace of this excitation induces the next grooming movement once the previous one is performed. This reveals a mechanism whereby parallel sensory inputs can be integrated and stored to elicit a delayed and sequential grooming response.

Motor sequences are formed through the serial execution of different movements, but how nervous systems implement this process remains largely unknown. We determined the organizational principles governing how dirty fruit flies groom their bodies with sequential movements. Using genetically targeted activation of neural subsets, we drove distinct motor programs that clean individual body parts. This enabled competition experiments revealing that the motor programs are organized into a suppression hierarchy; motor programs that occur first suppress those that occur later. Cleaning one body part reduces the sensory drive to its motor program, which relieves suppression of the next movement, allowing the grooming sequence to progress down the hierarchy. A model featuring independently evoked cleaning movements activated in parallel, but selected serially through hierarchical suppression, was successful in reproducing the grooming sequence. This provides the first example of an innate motor sequence implemented by the prevailing model for generating human action sequences., (Copyright © 2014, Seeds et al.)

Understanding the logic behind how a fruit fly's brain tells it to groom its body parts in a stereotyped order might help us understand other behaviours that also involve a series of actions., (Copyright © 2014, Yang and Clandinin.)