Neuropsychologia 44 (2006) 2520–2525

Postural control after a night without sleep

Marco Fabbri ∗, Monica Martoni, Maria Jose Esposito, Gianni Brighetti, Vincenzo NataleDepartment of Psychology, University of Bologna, Viale Berti Pichat, 5, Bologna 40127, Italy

Received 7 October 2005; received in revised form 14 March 2006; accepted 26 March 2006Available online 9 May 2006

Abstract

The present study analysed the efficiency of postural control after 12 h of nocturnal forced wakefulness using Romberg’s test comprising 1 minof recording with eyes-open and 1 min of recording with eyes-closed, with a 1 min break between the two sessions. Our aim was to see if thedecreased postural control efficiency after a sleepless night was unspecific (in both eyes-closed and eyes-open conditions) or selective (in onlyone of the conditions). A total of 55 students spent a whole night awake at our laboratory and were tested at 22:00 and 08:00 h. In general, theresults showed that postural sway increased, performing the recording from eyes-open to eyes-closed condition. The statokinesigram length (SLor efficiency of the postural system) increased after the sleepless night, while in eyes-open condition, the length in function of surface (LFS oraccuracy of postural control) and Romberg’s index (or contribution of vision to maintain posture) significantly decreased. This could indicate thatas©

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fter a night without sleep, there is a slower elaboration of visual inputs in the postural control process. On the basis of these results, the effects ofleep deprivation on cognitive performance were considered from a neuropsychological point of view.

2006 Elsevier Ltd. All rights reserved.

eywords: Alertness; Balance; Stabilometric platform; Cortico-thalamic area; Integration system; Mood

. Introduction

Postural control is determined by an interplay of visual,roprioceptive and vestibular inputs which are dynamicallyeighted to determine body position and maintain equilibrium.uch control requires attentional resources. To test this point,tudies using the dual-task paradigm have proved particularlyseful. Pellecchia (2003) asked subjects to maintain equilib-ium while performing three different kinds of tasks requiring

steadily increasing level of attention. Postural sways wereeasured by stabilometric platform and it was found that the

iggest postural change occurred when the most difficult taskas administered. In line with this study, Maki and McIlroy

1996) found postural sway increased as the attention load ofhe cognitive tasks given to the subjects increased. Teasdalend Simoneau (2001) studied the efficiency of postural con-rol during a dual-task in both young and elderly adults. Sub-ects were asked to perform a cognitive task while standing uptraight. As in previous studies, as the difficulty of the cogni-ive task increased, postural sway heightened because of a lack

of attentional resources. However, while lower postural con-trol efficiency during dual-task was found in both groups, theelderly subjects proved more sensitive to drops in attention levelsthan the younger subjects (and hence experienced more postu-ral sways) (Teasdale & Simoneau, 2001). It has been suggestedthat as age increases, postural control requires greater atten-tional resources (Fife & Baloh, 1993). This has been ascribedto the malfunctioning of visual (Nashner, Black, & Wall, 1982),vestibular (Norre, Forrez, & Beckers, 1987) and proprioceptive(Lord, Clark, & Webster, 1991) systems.

Some authors have not excluded the role of arousal as poten-tial puzzled factor affecting the efficiency of postural control.Arousal varies regularly over 24 h (circadian rhythm), but mightbe affected by other variables like sleep deprivation. In oursociety, many people have to work during the night so a nightwithout sleep is not an exceptional situation. Sleep deprivationinduces decreased subjective alertness and cognitive perfor-mance. Decreased alertness levels have been found with short-and long-term periods of sleep deprivation, using both objectiveand subjective measures of sleepiness (Harma et al., 1998). Thedrop in cognitive performance in simple (Gillberg & Akerstedt,

∗ Corresponding author. Tel.: +39 051 2091846; fax: +39 051 243086.E-mail address: marco.fabbri21@unibo.it (M. Fabbri).

1998) and complex (Harrison & Horne, 1997, 1998, 1999) taskswas present in the first night of sleep deprivation and increasedin the following nights.

028-3932/$ – see front matter © 2006 Elsevier Ltd. All rights reserved.

oi:10.1016/j.neuropsychologia.2006.03.033

M. Fabbri et al. / Neuropsychologia 44 (2006) 2520–2525 2521

Neuropsychological data show that after a night of sleepdeprivation, neuronal activity decreases mainly in the cortico-thalamic network, which mediates attention and higher ordercognitive performance (Thomas et al., 2000). In a night ofsleep deprivation, the bilateral posterior-parietal prefrontal areas(PFC) are less activated (Drummond et al., 1999; Thomas et al.,2000) prompting lower levels of activity in the central execu-tive system. This can affect executive functions such as mentalflexibility, behavioural inhibition, thinking and problem solving.

Changes in standing postures over 19, 24 and 48 h of contin-uous wakefulness have been explained by a drop in attentionlevels (Gribble & Hertel, 2004; Liu, Higuchi, & Motohashi,2001; Manganotti, Palermo, Patuzzo, Zanette, & Fiaschi, 2001;Nakano et al., 2001). The effect of sleep deprivation on postu-ral sways is correlated to drops in alertness levels (Liu et al.,2001), peaking when the body temperature reaches its negativepeak (Nakano et al., 2001). It is however still unclear how sleepdeprivation affects the efficiency of postural control.

Some studies have investigated the effects of sleep depriva-tion on postural control using centre of pressure (COP), centreof pressure area (COPA) and centre of pressure velocity (COPV)as stabilometric indexes (Caldwell, Prazinko, & Caldwell, 2003;Gribble & Hertel, 2004; Schlesinger, Redfern, Dahl, & Jennings,1998; Uimonen, Laitakari, Bloigu, & Sorri, 1994). The COPis the ratio between lateral and antero-posterior mean devi-ations of postural sways. The present study investigated theetTnMstbet(plfRifcan

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Fig. 1. The figure shows the indications for the standardised foot position onthe stabilometric platform (Beac Biomedical, 1999; modified). The silhouetteindicating where to position the feet (at a 30◦ angle) is drawn on the square-shaped platform surface. The three “g” points are the three “strain-gage” sensors,and they form an equilateral triangle of 40 cm. The x- and y-axes describe bothlateral and antero-posterior postural sways, respectively.

After a brief description of the study, subjects read and signed a written consentform.

2.2. Materials

Postural sways were measured by stabilometric platform, using the nor-malised balance platform (NBP) system (Beac Biomedical, 1999). The instru-ment, constructed in accordance with the specifications of the French Societyof Posturology (1986), comprised a smooth surface (600 mm × 600 mm). Three“strain-gage” sensors placed to form an equilateral triangle (400 mm × 400 mm)picked up the position of centre of mass projection. Signals were directly con-verted into digital data and sent to the computer through a serial RS232 link.The NBP software, using the WINDOWS interface, transformed the computerinto a polygraphic system. The spot where subjects had to position their feet wasindicated by a silhouette produced on the platform surface (Fig. 1).

This silhouette indicated where the feet (bare) should be placed, slightlyapart with heels joined so as to form a 30◦ angle. In this way, the bisectorangle formed by the feet was aligned with the sagittal axis of the platformand the centre of the polygon was positioned on this axis, 3.8 cm in front ofthe electric axis of the surface (Fig. 1). The French Society of Posturology(1986) has normalised standard values for subjects from 11 to 65 years. In theeyes-open position a projection of mass value of at least 200 mm2 is consideredacceptable. This value is calculated as the equilateral triangle area formed by thethree sensors. The stabilometric platform was placed in an internal white booth(100 cm × 130 cm × 240 cm) with a black fixation dot in front of the subjects.In this way, the subject was isolated from external inputs.

The global vigor and affect scale (GVA; Monk, 1989) comprising eight ques-tions was used as self-rating questionnaire for subjective alertness and moodlevels. The subjects were asked to score the intensity of their feelings along a10 cm line ranging from “not at all” to “very much”. Scores for tenseness, happi-ntwa

ffect of 12 h of forced nocturnal wakefulness on postural con-rol efficiency using Romberg’s test (Lanska & Goetz, 2000;hyssen, Brynskov, Jansen, & Munster-Swendsen, 1982), a testever used before for this purpose. This test is named afteroritz von Romberg, who described a patient with tabes dor-

alis presenting with complaints of increased unsteadiness inhe dark (Romberg, 1853). Romberg’s test has subsequentlyecome a commonly performed test in neurological studies tovaluate the spinal cord. In particular, Romberg’s test assesseshe functional integrity of the entire proprioceptive pathwayKhasnis & Gokula, 2003). At the beginning and end of theeriod of forced wakefulness in our study, we recorded meanateral deviation, antero-posterior mean deviation, support sur-ace, statokinesigram length, length in function of surface andomberg’s index. These parameters allowed us to quantify the

mpact of visual input on postural control comparing the per-ormance of eyes-open and eyes-closed conditions on the effi-iency of postural control. Subjective mood and alertness scorend body temperature level were also recorded throughout theight.

We expected a decrease in postural control after a wholeight without sleep. Manipulating the visual input enabled uso verify if the worsening performance is unspecific (in bothyes-closed and eyes-open conditions) or selective (in only onef the conditions).

. Method

.1. Subjects

The experimental sample comprised 55 volunteer students (mean age3.45 ± 3.29), 39 females (mean age 23.28 ± 3.59) and 16 males (23.87 ± 2.50).

ess, sadness and calmness were averaged and used to indicate mood state whilehe average scores for vigor, tiredness, effort for everyday tasks and sleepinessere used to measure alertness. Higher scores indicate better mood and greater

lertness.

2522 M. Fabbri et al. / Neuropsychologia 44 (2006) 2520–2525

A digital thermometer placed under the armpit was used to measure bodytemperature levels during the night and was employed as a physiologic index ofarousal levels (Adan, 1992).

2.3. Procedure

Volunteers arrived at 20:30 h and had to spend 12 consecutive hours at theLaboratory for Applied Chronopsychology, from 21:00 to 09:00 h. The experi-mental design envisaged 12 h of forced wakefulness during the night. The firststabilometric session was assessed at 22:00 h. Each subject was asked to getonto the platform and stare at the black dot. Subjects had to put their feet atthe point indicated by the silhouette and had to hold their arms at their sidesin a relaxed erect position. Romberg’s test is a technique that records postureand by interfering with the visual and proprioceptive sensory inputs during thistest, it can be determined just how sensory interaction is organised in balanc-ing the posture and equilibrium of the subject/patient examined (Norre, 1993).In a static posturograph, Romberg’s test was activated for a 1 min recording ineyes-open conditions. There was then a 1 min break before a 1 min recordingeyes-closed was performed in the same position. Each participant always per-formed the first task with his/her eyes-open for 1 min and the second task withhis/her eyes-closed for 1 min. The two recording conditions were not counter-balanced across subjects but they were kept in a constant order. Participantscompiled GVA and recorded their body temperature every 2 h (at 22:00, 24:00,02:00, 04:00, 06:00, 08:00 h). Subjects were kept awake by researchers dur-ing the night by means of didactic activities (i.e. lessons) on sleep and sleepdisorders. Coffee, tea, nicotine and light snacks were allowed during presched-uled breaks (generally 1 h before stabilometric task, GVA administration andtemperature recording) but alcohol and other psychoactive substances werestrictly forbidden. At the end of the sleepless night, a second stabilometricsession was performed at 08:00 h. All recordings were carried out in a silentr

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Fig. 2. Mean values of body temperature, alertness and mood ratings during thenight without sleep.

a Scheffe post-hoc test was carried out. Values with p < .05 were consideredsignificant.

3. Results

Results for body temperature are shown in Fig. 2. Theanalysis of variance carried out revealed a significant effectof time of day (F5,270 = 29.84−p < .00001). The post-hoc testindicated that body temperature was significantly greater at22:00 (36.69 ± 0.43) and at 24:00 h (36.56 ± 0.49) than at 02:00(36.35 ± 0.60), 04:00 (36.17 ± 0.61), 06:00 (36.19 ± 0.48) and08:00 h (36.24 ± 0.48) (p < .00001). As expected, body tempera-ture reached its lowest level at 04:00 h before increasing slightly.The body temperature at 08:00 h however was still significantlylower than at 22:00 h.

As regards subjective alertness (Fig. 2) the analysis ofvariance pointed to a significant effect of time of day(F5,270 = 61.65−p < .001). There was a significant differencebetween the first and last recording session. The Scheffe testshowed that alertness levels at 22:00 (76.83 ± 17.03) and at24:00 h (67.90 ± 18.63) were statistically higher (p < .00001)than those at 02:00 (57.04 ± 21.01), 04:00 (46.96 ± 21.04),06:00 (43.50 ± 22.30) and 08:00 h (44.82 ± 26.39). Subjectivealertness reached its lowest level at 06:00 h before increasingslightly. The subjective alertness level at 08:00 h however wasstill significantly lower than at 22:00 h.

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.4. Data analysis

Postural sways were measured using Romberg’s test (RT), analysing in par-icular mean deviation on lateral axis (MD-x), mean deviation on antero-posteriorxis (MD-y), support surface (SS), statokinesigram length (SL), length in func-ion of surface (LFS) and Romberg’s index (RI). MD-x (which in healthy peopleanges between −1 and + 1 cm) measures alterations in centre of mass load dis-ribution in both limbs, in sagittal axis (Baloh, Jacobson, Beykirch, & Honrubia,998). In the same way, MD-y (which in healthy subjects can vary by 15 cm)easures antero-posterior centre of mass imbalances (Baloh et al., 1998). TheS is calculated as the surface of an oval containing 90% of the centre of massrojection points on the platform surface. SS measures proprioceptive and cuta-eous inputs at the contact points where the feet touch the support surface, andauges the changes in orientation of a standing subject (Nashner et al., 1982). Inhealthy (without posturtal disorders) eyes-open subject, SS value should varyithin a range of 100 mm2 while in an eyes-closed subject a surface rangingp to 30 cm2 should be acceptable. The SL (or “length of clew”) is a measuref the effort needed to maintain an upright station and is a parameter which,inked to SS, measures the efficiency of the postural system. In other words,S being equal a lower SL involves a smaller expenditure of energy and henceore efficient postural control (Norre & Forrez, 1986). The LFS (surface length)as calculated as surface, in eyes-open/eyes-closed conditions, divided by eyes-pen/eyes-closed length of surface providing information about the accuracy ofostural control and the effort made by the subject. The RI (Romberg’s Index)s defined as the ratio between eyes-closed SS (SSc) and eyes-open SS (SSo)RR = SSc/SSo × 100). A higher RI score indicates a worse SSo versus SScerformance. This parameter reflects the contribution vision makes to maintainosture.

For the stabilometric parameters, such as MD-x, MD-y, SS, SL and LFS, aepeated measures ANOVA with time (two levels: at 22:00 and at 08:00 h) andisual input (eyes-open and eyes-closed conditions) as within-subjects factors,as carried out. We performed a comparative analysis between the first trial at2:00 and the second at 08:00 h using t-test, only for RI. For body temperature,ubjective alertness and mood, on the other hand, we performed a repeated mea-ures ANOVA (time of day at six levels). Where comparisons were significant,

The analysis of variance revealed a significant effect of timef day (F5,270 = 3.64−p < .005) on mood score too (Fig. 2).he post-hoc test showed that mood scores were meaning-

ully higher (p < .05) at 02:00 h (78.46 ± 12.85) than scores at4:00 (71.64 ± 15.01) and 06:00 h (71.74 ± 18.26). No differ-nce between the first and last experimental sessions were found.

The ANOVAs on MD-x, MD-y and SS scoreshowed that visual input factor was significant for MD-xF1,54 = 4.28−p < .05), MD-y (F1,54 = 7.89−p < .05) and SSF1,54 = 31.43−p < .00001). Generally, in eyes-open condition,he subjects had significantly lower scores than those in eyes-losed condition (MD-x: eyes-open = −0.79 ± 7.10 and eyes-losed = 0.36 ± 7.10; MD-y: eyes-open = −8.58 ± 12.94 and

M. Fabbri et al. / Neuropsychologia 44 (2006) 2520–2525 2523

Fig. 3. The changes of LFS values during a night without sleep in both eyeconditions.

eyes-closed = −5.31 ± 14.62; SS: eyes-open = 113.08 ± 92.01and eyes-closed = 172.43 ± 146.69). On the contrary, time fac-tor and time x visual input interaction did not reach significantlevels for these three stabilometric parameters. The ANOVA onSL illustrated a significance for time (F1,54 = 6.33−p < .05) andvisual input (F1,54 = 148.75−p < .00001) factors. At 22:00 h(489.28 ± 194.25), SL was significantly lower respect at08:00 h (529.55 ± 174.60). Comparing eyes-open/eyes-closedconditions, SL values were significantly lower in eyes-opencondition (407.75 ± 128.52) than in eyes-closed condition(611.08 ± 240.32). The interaction time x visual input did notreach any significant level. The ANOVA on LFS scores showedthat any factors reached significant levels while the interactionwas significant (F1,54 = 7.83−p < .05) (see Fig. 3). The post-hoctest showed that the LFS in eyes-open condition at 22:00 h(5.58 ± 3.38) was significantly (p < .05) higher respect to LFSin eyes-closed condition at 22:00 h (4.60 ± 2.36), and respect toLFS in eyes-open condition at 08:00 h (4.63 ± 2.23). The t-testcomparison on RI achieved significance (t54 = 2.48−p < .05).RI was significantly higher at 22:00 h (211.85 ± 175.71) thanat 08:00 h (148.69 ± 80.25).

4. Discussion

The aim of the present work was to study the effect of ansLvwopieptfor

icantly increased (worse performance) from the beginning tothe end of sleep deprivation and it significantly increased fromeyes-open to eyes-closed condition. Hence, the efficiency of thepostural system was affected by two main factors: a night offorced wake and the visual condition of recording. The accu-racy of postural control (LFS) decreased after the night withoutsleep. The interaction time x visual input showed how the perfor-mance only in eyes-open condition significantly decreased aftera night without sleep. When LFS (high values correspondedhigh accuracy) decreased, subjects found it harder to maintainan erect posture. Even if the comparison was not significant, theLFS values in eyes-closed condition tended to increase duringthe night. These findings could prove how the postural controlsystem worsened in integration of sensory input, maybe for thedecrease of attentional resources. Finally, Romberg’s index fellsignificantly at 08:00 h versus 22:00 h. RI is a function of theratio between SS eyes-closed and SS eyes-open so that a lowerRI would correspond to a performance that is fairly similar ineyes-closed/eyes-open conditions. We can conclude thereforethat after a night without sleep there is a reduction in the effi-ciency of postural control which is particularly marked in theeyes-open condition, as illustrated by LFS and RI. We cannotsay whether such a reduction is caused by a less efficient visualsystem per se or by a less efficient integration of visual input.We can however posit that after a night without sleep it is asif postural control was unable to use visual input. The sensoryic

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ight without sleep on postural control. In our study, posturalways were measured for the first time by MD-x, MD-y, SS, SL,FS and Romberg’s index, allowing us to compare eyes-openersus eyes-closed performances. The two recording conditionsere kept in constant order, according to standard proceduref Romberg’s test. The results illustrated, in general, how theerformance worsened when the subjects did the first record-ng with their eyes-open and the second recording with theiryes-closed. These findings proved the role of visual input forostural control system. Moreover, significant changes betweenhe beginning and end of nocturnal forced wakefulness wereound. The length of surface (SL) increased after the night with-ut sleep indicating that subjects had to use greater attentionalesources to correct their postural sways. The SL index signif-

ntegrated system in fact significantly worsens only in eyes-openondition.

The subjective and objective arousal data in our study, mon-tored throughout the night, agree with previous chronobiol-gy studies (Adan, 1992). The lack of any correlation betweenrousal data and stabilometric parameters in our research, dueo differences in recording conditions (six versus two condi-ions), means it is not possible to fully assess the relationshipetween alertness and postural change during a night of sleepeprivation from a chronobiological point of view. The mea-urement of subjective and objective vigilance levels, however,llows us to conclude that a drop in alertness can affect posturalontrol. The literature indicates that postural control efficiencyecreases during the night while postural sways can be corre-ated to sleepiness (Liu et al., 2001; Nakano et al., 2001). Inddition, some authors have claimed that the circadian phase ofody temperature might affect the efficiency of postural controlGribble & Hertel, 2004; Nakano et al., 2001), suggesting thathe time of day be taken into consideration when comparing

easures of postural control. As shown in Fig. 2, the subjectiveigilance and body temperature curves decreased in similar fash-on until the fourth session (at 04:00 h), with a small increase at8:00 h. The behavioural data on the other hand indicated moreostural sway at the end of sleep deprivation, perhaps due todecrease in attentional resources and increased sleepiness, as

eported in the literature. The role of mood states in the posturalontrol process finally has also been discussed in the literatureBolmont, Gangloff, Vouroit, & Perrin, 2002). Our data showedo differences between the mood scores at 22:00 and at 08:00 h,ndicating that postural control is perhaps not affected by moodariation during a night of sleep deprivation. Our sample did not

2524 M. Fabbri et al. / Neuropsychologia 44 (2006) 2520–2525

include clinical patients, as was the case in the study by Bolmontet al. (2002). Future research is needed to clarify the effect ofalertness on postural control after a normal night of sleep.

Postural control is determined by a continuous integrationof visual, vestibular and proprioceptive inputs (Teasdale &Simoneau, 2001). After a complete night of forced wake, theintegration system is altered, perhaps because of a drop in alert-ness levels, meaning that the postural control system is unableto use visual input to maximum advantage. A possible rea-son for this lack of sensory integration may be ascribed to theoverlapping of neuropsychological data during sleep depriva-tion and during maintenance of upright posture. In 24 h of sleepdeprivation Thomas et al. (2000) and Drummond et al. (1999)found deactivation of the cortico-thalamic network, promptingalteration of the attentional system and prefrontal cortex func-tions. A report on the effects of 32 h of sleep deprivation (Wuet al., 1991) measured the metabolism of cerebral glucose andfound lower metabolic rates in the temporal lobes (vestibularsystem), thalamus, basal ganglia (proprioceptive system), whitematter and cerebellum (proprioceptive system). Furthermore,reduced visual alertness proved to be significantly correlatedwith reduced metabolic rates in thalamic, basal ganglia and lim-bic regions (Wu et al., 1991). In another study investigatingthe cortical areas involved in maintaining upright posture, spe-cific areas in the cerebellum (cerebellar vermis efferent system)and the visual associative cortex were activated (Ouchi, Okada,Yai2via

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Drummond, S. P. A., Brown, G. G., Stricker, J. L., Buxton, R. B., Wong, E.C., & Gillin, J. C. (1999). Sleep deprivation-induced reduction in corticalfunctional response to serial subtraction. Neuroreport, 10, 3745–3748.

Fife, T. D., & Baloh, R. W. (1993). Disequilibrium of unknown cause inolder people. Annuals Neurology, 34, 694–702.

French Society of Posturology. (1986). Statistical studies of measurementsmade on normal man using the standardised platform of clinical stabilom-etry. (I) Spatial parameters. Agressologie, 27, 69–72.

Gillberg, M., & Akerstedt, T. (1998). Sleep lost and performance: No safeduration of a monotonous task. Physiology and Behaviour, 64, 599–604.

Gribble, P. A., & Hertel, J. (2004). Changes in postural control during a 48-hr.sleep deprivation period. Perceptual and Motor Skills, 99, 1035–1045.

Harma, M., Suvanto, S., Popkin, S., Pulli, K., Mulder, M., & Hirvonen,K. (1998). A dose-response study of total sleep time and the ability tomaintain wakefulness. Journal of Sleep Research, 7, 167–174.

Harrison, Y., & Horne, J. A. (1997). Sleep deprivation affects speech. Sleep,20, 871–877.

Harrison, Y., & Horne, J. A. (1998). Sleep loss impairs short and novellanguage tasks having a prefrontal focus. Journal of Sleep Research, 7,95–100.

Harrison, Y., & Horne, J. A. (1999). One night of sleep loss impairs inno-vative thinking and flexible decision making. Organic Behaviour andHuman Decision Processes, 78, 128–145.

Khasnis, A., & Gokula, R. M. (2003). Romberg’s test. Journal of Postgrad-uate Medicine, 49, 169–172.

Lanska, D. J. (2002). The Romberg sign and early instruments for measuringpostural sway. Seminars in Neurology, 22, 409–418.

Lanska, D. J., & Goetz, C. G. (2000). Romberg’s sign. Development, adop-tion, and adaptation in the 19th century. Neurology, 55, 1201–1206.

Liu, Y., Higuchi, S., & Motohashi, Y. (2001). Changes in postural swayduring a period of sustained wakefulness in male adults. Occupational

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oshikawa, Nobezawa, & Futatsubashi, 1999). The brain areasctivated during postural control are therefore less activated dur-ng sleep deprivation (Drummond et al., 1999; Thomas et al.,000). It may therefore be hypothesised that there is minor acti-ation of the thalamus and the prefrontal cortex that causes thenput integration problems due to a lack of attentional resourcesnd reduced supervising function.

In conclusion, our data confirm that a complete night of forcedakefulness prompts postural sway, probably as a result of

hanged sensory system integration, especially of visual inputs.n explanation for this may lie in the deactivation of brain areasediating attention and supervision. We wonder whether this

ifficulty in elaborating/integrating visual input after a nightithout sleep only affects postural control or whether it modu-

ates all reductions in cognitive performance observed after sleepeprivation. Further studies are needed to investigate this point.

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