Effects of neck flexion on contingent negative variation and anticipatory postural control during arm movement while standing

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Abstract

We investigated the effects of neck flexion on contingent negative variation (CNV) and anticipatory postural control using an arm flexion task in standing. CNV was adopted to evaluate the state of activation of brain areas related to anticipatory postural control. Subjects were required to flex the arms in response to a sound stimulus preceded by a warning sound stimulus. Two different intervals (2.0 and 3.5 s) between these two stimuli were used in neck position in quiet standing (neck resting) and neck position at 80% angle of maximal neck flexion. The mean amplitude of CNV 100-ms before the response stimulus, recorded from a Cz electrode, was calculated. Onset timing of activation of the postural muscles (lumbar paraspinal, biceps femoris and gastrocnemius) with respect to the anterior deltoid was analyzed. Reaction time at the anterior deltoid was significantly shorter in the 2.0 s period than in the 3.5 s period, and in the neck flexion than in the neck resting in both periods. In the 2.0 s, but not in the 3.5 s period, neck flexion resulted in an increased CNV amplitude and an increased duration of preceding activation of the postural muscles, and the correlation between these increases was significant.

Introduction

Many studies have shown that when the arm is flexed by a standing subject, the postural muscles of the legs and trunk that control standing posture are activated in advance of the focal muscles that move the arm rapidly (Belen’kii et al., 1967). It has been presumed that this preceding activation of the postural muscles is controlled by a program selected in advance so as to moderate any disturbances of posture and equilibrium caused by the arm movement (El’ner, 1973, Horak et al., 1984, Friedli et al., 1984). Clinical research has shown that this type of postural control, known as anticipatory postural control, is probably associated with the higher levels of the central nervous system, particularly the supplementary motor and premotor areas (Gurfinkel and El’ner, 1988, Massion et al., 1999, Viallet et al., 1992). One of the indices of activation of these brain areas is contingent negative variation (CNV) (Ikeda et al., 1997, Gemba et al., 1990, Lamarche et al., 1995). A paradigm of warning stimulus – response stimulus – motor response has been used to investigate CNV, and in this paradigm, CNV is observed as a slow negative brain potential which is obtained by averaging electroencephalograms (EEGs) during the period between warning and response stimuli (Walter et al., 1964).

In an earlier study, we investigated both CNV and anticipatory postural control during upper limb movement performed in the standing posture, and found that the late component of CNV amplitude (late CNV) increased when prediction of the response stimulus was relatively easy due to a short preparatory period (2.0 s), and that increases in CNV amplitude and changes in the preceding activation time of the postural muscles were related. However, in longer preparatory period than 3.0 s, prediction of the response stimulus was relatively difficult and the amplitude of late CNV decreased. Preceding activation of the postural muscles was, however, observed in this preparatory period (Maeda and Fujiwara, 2007). Other researchers, however, have observed no preceding activation of the postural muscles when prediction of the response stimulus is difficult (De Wolf et al., 1998, Woollacott et al., 1984). We therefore suggested that preceding activation of an alternative postural strategy was employed when prediction of the response stimulus was relatively difficult.

We have found that reaction times for saccadic eye movements (Fujiwara et al., 2000) and finger flexion (Fujiwara, 1994) are shorter in a neck flexion posture (neck flexion angle from 5° to 25°) than in a natural neck posture (0°). We also found that the shortening of saccadic reaction time during vibratory stimulation of the neck extensors was similar to that produced by moderate isometric contraction of the shoulder girdle elevators, and we suggested that this was the result of an increase in afferent information from the neck muscles (Fujiwara et al., 2001). We have also observed an increase in spinal motor neuron excitation (Fujiwara et al., 1998), shortening of the P100 latency of visual evoked potential (Kunita and Fujiwara, 2004), and an increase in the amplitude of the middle-latency auditory evoked potential (Fujiwara et al., 2005) during neck flexion. These changes are considered to result from an extensive activation of the central nervous system (Klemm, 1990, Magoun, 1964, Vallar et al., 1995), and we hypothesize that with neck flexion such activation occurs in the supplementary motor and premotor areas, and should be reflected in an increase in late CNV. We also postulate that when it is difficult to predict the timing of a response stimulus, both CNV and preceding activation of the postural muscles will not change with neck flexion.

In this work, we investigate the effects of neck flexion on CNV and anticipatory postural control using an arm flexion task in a standing subject. The working hypothesis is that the effect of neck flexion on both late CNV and the preceding activation of postural muscles will differ according to the length of the preparatory period.

Section snippets

Subjects

Subjects were eight women and six men, aged 19–29 years (mean age 23.8; SD = 3.1). No subject displayed any history of neurological or orthopedic impairments. Informed consent was obtained from all subjects following an explanation of the experimental protocols. Mean height, mass, and foot length were 165.0 cm (SD = 8.2), 58.9 kg (SD = 8.2) and 24.8 cm (SD = 1.6), respectively.

Equipment

All measurements were taken with subjects standing barefoot, with feet 10 cm apart and parallel on a force platform (OR6-6; AMTI,

AD reaction time

In the 2.0 s preparatory period, AD reaction time was 134.5 ms (SD = 13.8) in the neck resting condition and 127.5 ms (SD = 15.6) in the neck flexion condition, while in the 3.5 s preparatory period, the AD reaction times were 150.4 ms (SD = 15.8) and 135.9 ms (SD = 12.7), respectively. Significant main effects of neck posture and preparatory period on reaction time were obtained (neck posture: F1,39 = 26.5, p < 0.001, preparatory period: F1,39 = 13.9, p < 0.01), and there was no significant interaction between the

Discussion

In the 3.5 s period as compared with the 2.0 s preparatory period, late CNV amplitude was significantly smaller and reaction time of the anterior deltoid was significantly longer. Our previous study demonstrated similar results, with 3.0 s being the cut-off point for differences depending on preparatory period (Maeda and Fujiwara, 2007). Moreover, in a tapping task performed in response to cyclic click sounds, the response pattern changed from the expected response to a delayed response when the

Acknowledgement

This work was supported by Grant-in-Aid for Scientific Research (A) (17207019).

Katsuo Fujiwara received his PhD from Tsukuba University in 1984. He is a professor at the Department of Human Movement and Health, Graduate School of Medical Science, Kanazawa University (2001–Present). He is a member of the International Society of Electrophysiological Kinesiology, the International Society of Posture and Gait Research, and the Society for Neuroscience. He serves as permanent director of the Japanese Society of Health and Behavior Science. He is now analyzing the anticipatory

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  • Cited by (0)

    Katsuo Fujiwara received his PhD from Tsukuba University in 1984. He is a professor at the Department of Human Movement and Health, Graduate School of Medical Science, Kanazawa University (2001–Present). He is a member of the International Society of Electrophysiological Kinesiology, the International Society of Posture and Gait Research, and the Society for Neuroscience. He serves as permanent director of the Japanese Society of Health and Behavior Science. He is now analyzing the anticipatory processes of postural control in the brain by using electromyograms, evoked potentials, event-related potentials, and cerebral blood flow.

    Hidehito Tomita received his Bachelor’s degree in Health Science from Kanazawa University in 2000. Since 2005 he has been a doctor course student at Kanazawa University. He is currently performing research into the relationship between anticipatory postural control and visuo-spatial attention in Dr. Fujiwara’s laboratory.

    Kaoru Maeda received his PhD from Kanazawa University in 2006. He has been studied on a relationship between postural control and contingent negative variation. His current interest is on changes in motor preparation state before postural perturbation, and now conducting a research on that theme under the leadership of coauthor Dr. Fujiwara.

    Kenji Kunita received his PhD from Kanazawa University in 1997. He is an associate professor at Research Center for Urban Health and Sports, Osaka City University (2007–Present). He is a member of the International Society of Posture and Gait Research, and the Society for Neuroscience. He is now analyzing the activation of the brain associated with neck flexion.

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