Repeated Bout Rate Enhancement Is Elicited by Various Forms of Finger Tapping

Abstract

Voluntary rhythmic movements, such as, for example, locomotion and other cyclic tasks, are fundamental during everyday life. Patients with impaired neural or motor function often take part in rehabilitation programs, which include rhythmic movements. Therefore, it is imperative to have the best possible understanding of control and behaviour of human voluntary rhythmic movements. A behavioural phenomenon termed repeated bout rate enhancement has been established as an increase of the freely chosen index finger tapping frequency during the second of two consecutive tapping bouts. The present study investigated whether the phenomenon would be elicited when the first bout consisted of imposed passive finger tapping or air tapping. These two forms of tapping were applied since they can be performed without descending drive (passive tapping) and without afferent feedback related to impact (air tapping) – as compared to tapping on a surface. Healthy individuals (n = 33) performed 3-min tapping bouts separated by 10 min rest. Surface electromyographic, kinetic, and kinematic data were recorded. Supportive experiments were made to measure, for example, the cortical sensory evoked potential (SEP) response during the three different forms of tapping. Results showed that tapping frequencies in the second of two consecutive bouts increased by 12.9 ± 14.8% (p < 0.001), 9.9 ± 6.0% (p = 0.001), and 16.8 ± 13.6% (p = 0.005) when the first bout had consisted of tapping, passive tapping, and air tapping, respectively. Rate enhancement occurred without increase in muscle activation. Besides, the rate enhancements occurred despite that tapping, as compared with passive tapping and air tapping, resulted in different cortical SEP responses. Based on the present findings, it can be suggested that sensory feedback in an initial bout increases the excitability of the spinal central pattern generators involved in finger tapping. This can eventually explain the phenomenon of repeated bout rate enhancement seen after a consecutive bout of finger tapping.

Effect of Tapping Bout Duration During Freely Chosen and Passive Finger Tapping on Rate Enhancement

“…Thus, the first tapping bout can be considered to act as an initial kind of 'priming' of a second tapping bout. The RBRE phenomenon was recently replicated (Emanuelsen et al, 2018;Mora-Jensen et al, 2017). It has been speculated, that an increase of the freely chosen finger tapping rate in the second bout reflects an increase of CPG-mediated movement rate output (Hansen & Ohnstad, 2008;Shima et al, 2011).…”

“…Next, a demonstration was done by the experimenter on how to perform finger tapping and on the test procedure in general. The participant was shown and explained how to perform tapping with the index finger of the right hand at a freely chosen rate, while the remaining four fingers of the right hand were relaxed, extended and in contact with the table (Emanuelsen et al, 2018;Hansen et al, 2015;Mora-Jensen et al, 2017;Sardroodian et al, 2016). It was emphasized to the participant that tapping was not required to be performed at a constant rate or as fast as possible, but rather at "a comfortable rhythm" or at "an individually preferred rhythm" while at the same time "thinking about something else".…”

“…Participants who showed RBRE from the first to the second bout in the baseline tapping session were selected for participation in four additional tapping sessions applying either active or passive tapping as priming. In line with previous work by Emanuelsen et al (2018), a criterion of a minimum increase of 3% of the freely chosen tapping rate from the first to the second bout was applied.…”

“…Thereafter, the LED-tracker was mounted as described for the baseline tapping session. Then, passive finger tapping in the first bout was applied to the index finger using a custom-built machine with a rocker arm (see Emanuelsen et al (2018) for photo and detailed information). The participant was instructed to "relax as much as possible" while the tip of the right index finger was placed at the end of the rocker arm, in conformity with Emanuelsen et al (2018).…”

“…For clarity, the formulation of increased net excitability includes both the possibility of an increase in facilitation of supraspinal structures, CPGs, and motoneurons as well as a decrease in inhibitory input to the mentioned parts of the nervous system. Furthermore, a recent study investigated the effect of passive finger tapping (obtained by using a machine to move the finger) on RBRE (Emanuelsen et al, 2018). Based on that study, it was suggested that sensory feedback alone during the first bout was sufficient to increase the net excitability and result in an increased tapping rate in a subsequent bout of freely chosen tapping.…”