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Automated postural responses are modified in a functional manner by instruction.

Weerdesteyn V, Laing AC, Robinovitch SN - Exp Brain Res (2008)

Bottom Line: The restoration of upright balance after a perturbation relies on highly automated and, to a large extent, stereotyped postural responses.It is still unknown, however, how the central nervous system deals with situations in which the postural response is not necessarily helpful in the execution of a task.However, when a specific balance recovery response is not desired after a perturbation, postural responses can be selectively downregulated and integrated into the motor output in a functional and goal-oriented way.

View Article: PubMed Central - PubMed

Affiliation: Department of Rehabilitation, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands. v.weerdesteyn@reval.umcn.nl

ABSTRACT
The restoration of upright balance after a perturbation relies on highly automated and, to a large extent, stereotyped postural responses. Although these responses occur before voluntary control comes into play, previous research has shown that they can be functionally modulated on the basis of cognitive set (experience, advanced warning, instruction, etc.). It is still unknown, however, how the central nervous system deals with situations in which the postural response is not necessarily helpful in the execution of a task. In the present study, the effects of instruction on automated postural responses in neck, trunk, shoulder, and leg muscles were investigated when people were either instructed to recover balance after being released from an inclined standing posture [balance recovery (BR) trials], or not to recover at all and fall onto a safety mattress in the most comfortable way [fall (F) trials], in both backward and leftward directions. Participants were highly successful in following the instructions, consistently exhibiting stepping responses for balance recovery in BR trials, and suppressing stepping in the F trials. Yet EMG recordings revealed similar postural responses with onset latencies between 70 and 130 ms in both BR and F trials, with slightly delayed responses in F trials. In contrast, very pronounced and early differences were observed between BR and F trials in response amplitudes, which were generally much higher in BR than in F trials, but with clear differentiation between muscles and perturbation directions. These results indicate that a balance perturbation always elicits a postural response, irrespective of the task demands. However, when a specific balance recovery response is not desired after a perturbation, postural responses can be selectively downregulated and integrated into the motor output in a functional and goal-oriented way.

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Average onset latencies (± SE) in response to backward and leftward perturbations for left and right sternocleidomastoid (SCL and SCR), anterior deltoid (DAL and DAR), posterior deltoid (DPL and DPR), rectus abdominis (ABL and ABR), rectus femoris (RFL and RFR), and tibialis anterior (TAL and TAR). Data from balance recovery trials are shown as black diamonds, and data from fall trials are shown as gray squares. * P < 0.01
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Fig2: Average onset latencies (± SE) in response to backward and leftward perturbations for left and right sternocleidomastoid (SCL and SCR), anterior deltoid (DAL and DAR), posterior deltoid (DPL and DPR), rectus abdominis (ABL and ABR), rectus femoris (RFL and RFR), and tibialis anterior (TAL and TAR). Data from balance recovery trials are shown as black diamonds, and data from fall trials are shown as gray squares. * P < 0.01

Mentions: Onsets of EMG activity in response to the perturbation could generally be detected in all the muscles within 200 ms. In backward BR trials, neck, trunk and leg muscles showed similar onsets (70–80 ms after tether release), followed by DPL and DPR at 80–90 ms and DAL and DAR at 90–100 ms, on average (Fig. 2). In the backward F trials, the overall mean onset latencies of the 12 muscles measured were delayed by 4.1 ms (SE 2.4 ms) compared to the BR trials [F(1,8) = 5.601, P = 0.045, Fig. 2]. At the level of the individual muscles, onsets were not significantly different between the instructions (all P values > 0.045). As can be seen from Fig. 2, the overall activation sequence remained similar between instructions.Fig. 2


Automated postural responses are modified in a functional manner by instruction.

Weerdesteyn V, Laing AC, Robinovitch SN - Exp Brain Res (2008)

Average onset latencies (± SE) in response to backward and leftward perturbations for left and right sternocleidomastoid (SCL and SCR), anterior deltoid (DAL and DAR), posterior deltoid (DPL and DPR), rectus abdominis (ABL and ABR), rectus femoris (RFL and RFR), and tibialis anterior (TAL and TAR). Data from balance recovery trials are shown as black diamonds, and data from fall trials are shown as gray squares. * P < 0.01
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2279151&req=5

Fig2: Average onset latencies (± SE) in response to backward and leftward perturbations for left and right sternocleidomastoid (SCL and SCR), anterior deltoid (DAL and DAR), posterior deltoid (DPL and DPR), rectus abdominis (ABL and ABR), rectus femoris (RFL and RFR), and tibialis anterior (TAL and TAR). Data from balance recovery trials are shown as black diamonds, and data from fall trials are shown as gray squares. * P < 0.01
Mentions: Onsets of EMG activity in response to the perturbation could generally be detected in all the muscles within 200 ms. In backward BR trials, neck, trunk and leg muscles showed similar onsets (70–80 ms after tether release), followed by DPL and DPR at 80–90 ms and DAL and DAR at 90–100 ms, on average (Fig. 2). In the backward F trials, the overall mean onset latencies of the 12 muscles measured were delayed by 4.1 ms (SE 2.4 ms) compared to the BR trials [F(1,8) = 5.601, P = 0.045, Fig. 2]. At the level of the individual muscles, onsets were not significantly different between the instructions (all P values > 0.045). As can be seen from Fig. 2, the overall activation sequence remained similar between instructions.Fig. 2

Bottom Line: The restoration of upright balance after a perturbation relies on highly automated and, to a large extent, stereotyped postural responses.It is still unknown, however, how the central nervous system deals with situations in which the postural response is not necessarily helpful in the execution of a task.However, when a specific balance recovery response is not desired after a perturbation, postural responses can be selectively downregulated and integrated into the motor output in a functional and goal-oriented way.

View Article: PubMed Central - PubMed

Affiliation: Department of Rehabilitation, Radboud University Nijmegen Medical Centre, PO Box 9101, 6500 HB Nijmegen, The Netherlands. v.weerdesteyn@reval.umcn.nl

ABSTRACT
The restoration of upright balance after a perturbation relies on highly automated and, to a large extent, stereotyped postural responses. Although these responses occur before voluntary control comes into play, previous research has shown that they can be functionally modulated on the basis of cognitive set (experience, advanced warning, instruction, etc.). It is still unknown, however, how the central nervous system deals with situations in which the postural response is not necessarily helpful in the execution of a task. In the present study, the effects of instruction on automated postural responses in neck, trunk, shoulder, and leg muscles were investigated when people were either instructed to recover balance after being released from an inclined standing posture [balance recovery (BR) trials], or not to recover at all and fall onto a safety mattress in the most comfortable way [fall (F) trials], in both backward and leftward directions. Participants were highly successful in following the instructions, consistently exhibiting stepping responses for balance recovery in BR trials, and suppressing stepping in the F trials. Yet EMG recordings revealed similar postural responses with onset latencies between 70 and 130 ms in both BR and F trials, with slightly delayed responses in F trials. In contrast, very pronounced and early differences were observed between BR and F trials in response amplitudes, which were generally much higher in BR than in F trials, but with clear differentiation between muscles and perturbation directions. These results indicate that a balance perturbation always elicits a postural response, irrespective of the task demands. However, when a specific balance recovery response is not desired after a perturbation, postural responses can be selectively downregulated and integrated into the motor output in a functional and goal-oriented way.

Show MeSH