Indian J Physiol Pharmacol 1998; 42(1): 57-63

AUTONOMIC CHANGES WHILE MENTALLY REPEATING TWOSYLLABLES - ONE MEANINGFUL AND THE OTHER NEUTRAL

SHIRLEY TELLES'. R. NAGARATHNA AND H. R. NAGENDRA

ViIJekarta"da Kendra Yoga Research Foundation,19, Eknath Bhuuan,K. G. Nagar, Bangalore - 560 019

(Received 00 July 7, 1997)

Abstract: Autonomic lind respiratory variables were recorded in 12volunteers in three types of sessions (1). Before, during and after a testperiod of mentally repeating 11 meaningful syllable 'OM' (MOM session)(2). A similar session except that the test period was spent mentallyrepeating II neutral work, 'one' (COM session) (3). A session with non­targeted thinking (NT session). The subjects were familiar with bothsyllables, and had been meditating on 'OM' for 20 days. During the testperiods of both MOM and COM sessions the rate of respiration (RR) andheart rate (HR) decreased significantly [(two factor ANOYA (RR), pairedt test (RR. HR)1. Compared to the pre period. Mental repetition of 'OM'(but not 'one') caused a significant decrease in skin resistance level (SRL)(paired t test). This was taken to mean that the subject recognized thesignificance of the syllable. No significant change occured during NTsessions.

Key words: relevant syllable

irrelevant syllable

skin resistance breath rate

heart rate

INTRODUCTION

The syllable 'OM' is known to haveprofound significance in Indian culture.Mental repetition of this syllabic was shownto cause significant changes in middlelatency auditory evoked potentials, whichwere suggestive of a facilitation of neuralactivity at either mesencephalic ordiencephalic level (1). In contrast mentallyrepeating a neutral syllable, 'one', inhibitedneural activity at the same level. This wasobserved in subjects who had been regularlymeditating on 'OM' every day for more than10 years ('experienced meditators'). In 'naive'

'Corresponding Author

subjects, with 15 to 20 days of experience inmeditation, repeating both 'OM' and 'one'caused the same effect, viz an inhibition ofneural activity at mesencephalic ordiencephalic level.

It was also reported that highlyexperienced meditators (20 years experienceon an average) show a significant reductionin heart rate and a non significant trend ofreduction in oxygen consumption, whilementally repeating 'OM', compared to aperiod of non targeted thinking (2). Thesesubjects simultaneously displayed an

58 Telles et al

increase in cutaneous vasoconstriction,which was interpreted as an increase inmental alertness (3), in the presence of othersigns of reduced arousal (reduced heart rateand oxygen consumption).

The present study was conducted tocompare the autonomic effects of mentallyrepeating a meaningful syllable with mentalrepetition of a neutral one and with nontargeted thinking, in subjects who wereacquainted with both syllables, and had beenmeditating on the meaningful syllable for20 days, comparable to the naive subjectsdescribed earlier 0), The duration ofmeditation was believed to influence theability to comprehend the significance of thesyllable and a comparison with resultsobtained in experienced meditators, could bemade.

METHODS

Subjects: There were 12 volunteers (4male, 8 female) with normal health asdetermined by a routine medicalexamination and ages ranging from 25 to 40years (Mean 30.1, SO 6.2 years). They hadbeen practicing 'OM' meditation for 20 daystwice a day, 15 min at a time, prior totesting. During a meditation session,subjects would keep their eyes closed andmentally repeat the syllable.

Design of the study: The subjects wereassessed in 3 separate sessions conductedon different days, at the same time of theday. Each session lasted for 25 min. The testperiod was for 15 min, while the 2 periodspreceding and following it, were for 5 mineach. For all 3 sessions subjects, remainedrecumbent (supine) with their eyes closed

Indian J Physiol Pharmacal 1998; 42(l)

while recording the 'pre' and 'post' periods.Instructions during the 'test' period (15 min)differed among the the 3 sessions. In thefirst 8 min of the 'OM' repetition session(MOM) subjects were given instructionsusing a prerecorded audio tape, to relax thebody from the toes upwards, naming eachpart of the body. The next 7 min of the 15min period were spent in mentally repeating'OM'. During the test period of the 'control'session (COM), the same sequence wasfollowed, i.e. 8 min following the sameprerecorded instructions to relax as for theMOM session, followed by 7 min of mentallyrepeating 'one'. During the session with nontargeted thinking (NT), subjects spent thefirst 8 min of the test period following thesame prerecorded instructions as for MOMor COM test periods. The next 7 min werespent in non targeted thinking. These twoperiods (8 min of guided relaxation and 7min of specific practice) were decided upon,as subjects reported that they were abole torelax while continuously repeating a syllablementally for a given period, when it waspreceded by guided relaxation. The dataacquired during the 15 min period as a wholewere analyzed. Also, the data obtainedduring the first 8 min (quided relaxation)and during the next 7 min ('OM'/'one'repetition/non targeted thinking) wereexamined separately to note any significantchange during either period.

The order of the 3 sessions (MOM, COM,NT) was varied in a random fashion for thesubjects. Hence 4 subjects had MOM sessionson day 1, with COM and NT sessions on thenext 2 consecutive days. Anotherr 4 subjectshad sessions in the order COM, NT, MOM.The 4 remaining subjects followed the orderNT, MOM, COM.

Indian J Physiol Pharmacal 1998; 42{l)

Recording conditions and parameters:The sessions were conducted in a dimly lit,sound attenuated cabin. A model 10polygraph (Recorders and Medicare,Chandigarh, India) was used to record theEKG, respiration, digit pulse volume (OPV)and skin resistance (SR). EKG was recordedusing the standard bipolar limb lead Iconfiguration and an AC bioamplifier with1.5 Hz high pass and 75 Hz low passsettings. Respiration was monitored with avolumetric pressure transducer. The subjectwas asked to stand erect and the transducerwas fixed around the trunk, 5 cm below thelower costal margin. A photoplethysmogramwas placed on the volar surface of the distalphalanx of the left index finger to assessthe digit pulse volume (DPV). Skinresistance (SR) was recorded using Ag/AgCldisk electrodes attached to the volar surfacesof the distal phalanges of the right indexand middle fingers, with a referenceelectrode on the volar surface of the rightforearm. Electrode gel (Medicon, Madras,India) was used, and a constant current of10 pA was passed between the electrodes.The signal was processed through a DCpreamplifier. The EEG was recorded withAg/AgCI disk electrodes placed at F3, F4, 01and 02 (4), each referenced to thecontralateral earlobe. The EOG and EMGwere recorded as for standardpolysomnography (5). For EEG and EOG thetime constant was 0.1 s, for EMG it was1.0 s). Recordings of EEG. EOG and EMGallowed any sleep episodes to be detectedwith the purpose of excluding them fromanalysis.

Data acquisition and analysis: The skinresistance (SR) trace was sampled every30 s. The amplitude of the digit pulse wassampled from the ascending portion of the

Autonomic Changes while Repeating Syllables 59

wave at 30 s intervals and converted to mVas described elsewhere (6). The heart rate(HR) was calculated by counting the QRScomplexes in successive 60 s epochscontinuously, to give the HR in beats permin (bpm). The rate of respiration (RR) wassimilarly calculated by counting the numberof respiratory waves also in successive60 s epochs continuously, and noting the RRas cycles per min (cpm).

Data were analyzed in two ways: (i) atwo factor ANOVA using data obtained inthe 'pre' and 'test' periods, but not in the'post' period. The ANOVA was used toexamine two factors, viz. a) the two states('pre' versus 'test' - Factor A) and b) thethree sessions (MOM, COM, NT - FactorB). The multiple comparison Tukey test('least significant difference' test) was usedto make pairwise comparisons, e.g. 'pre'(MOM) versus 'test' (MOM).

(ij) The 't' test for paired data was usedto compare the data of 'test' and 'post'periods with those of the corresponding 'pre'period.

RESULTS

General remarks: No sleep episodes weredetected and hence the entire record wasused for analysis. There were also (i) nosignificant changes in any of the parametersduring the first 8 min (guided relaxation) ofthe 'test' periods, compared to the 'pre'periods, and (ii) the (non significant)changes observed during the first 8 min ofthe 'test' period did not differ among the 3sessions. It was decided to use the data ofthe next 7 min of the 'test' period ('OM'I'one' repetition/non targeted thinking) for

60 Telles et aJ

statistical analysis, so that the duration ofthis period (7 min) was comparable to that.of the 'pre' and ;post' periods (5 min). Thegroup mean values ± SEM are provided inTable L

Indian J Physiol Pharmacol1998; 42(1)

interaction between the Factors Le. A x B(P>.10, in both cases). For the remainingparameters (heart rate, digit pulse volumeand skin resistance level), the two factorANOVA did not show significant differences

TABLE ; Autonomic variables during pre, test and post periods of MOM, 'OM' repetition, COM, 'one'

repetition, and NT, non targeted thinking sen ions. Values are group mean :I: SEJl.1.

Session

MOM

COM

NT

Period Hearl rate Digil pulse Skin Breath rOle

(bplll) 1I011lllle (m V) resistance (K) (cpmJ

p" 70.0:1: 1.9 1.4:1: 0.3 151.0 :1:32.3 15.5:1: 1.7

Test 66.6 % 2.3' 1.6:1: 0.3 121.0" :I: 26.8 12.9:1: 1.2'"

Post 70.9:1: 2.2 1.1:1: 0.2 99.0'" :I: 32.3 13.5:1: 1.7'

p" 70.9:1: 1.8 2.0:1: 0.2 170.0:1: 35.2 15.1 .% 1.3

Tesl 69.4 :t: 2.0' 2.1:t: 0.1 177.0 :1:42.3 lOA .% 1.3'"

Post 69.3:1: 1.9' 1.6:1: 0.1 182.0:1: 42.4 13.3 :t: 1.5'

P,. 70.4 :I: 1.9 1.8:1: 0.1 165.0:t37.8 14.9 :t 1.4

Test 69.9:t: 1.8 1.9:1:-0.1 166.0:1: 37.4 14.1:1: 1.6

Post 70.9:t: 1.8 1.5:1:0.1 144.0:1: 36.9 14.5:1:- 1.5

'P<.05, "P<.OI, '''P<.OOI paired 't' test, compared to pre.

Two factor ANOVA: The two factorANOVA showed a significant differencebetween the respiratory rate (RR) of 'pre'and 'test' periods, i.e. Factor A = 'pre' versus'test' IF = 5.28 (F.05 (2) 1, 66 = 5.27) hencep < .05 or P = .05]. The F value has beenderived by linear interpolation according tothe method described (7), based on the Fvalues for OF = 1,60 and DF = 1, 70 in thestandard table. The Tukey multiplecomparison test did not reveal a significant.difference between any two mean values. Inall comparisons q was less than 3.50, [sinceq (6, 60) = 3.75 at .10 level, therefore P>.10].Here 60 is utilized as t.he next critical valueafter 66, which is not. listed in the table.

There was no significant differencebetween the 3 sessions (Factor B), or of

between the values of 'pre' and 'test' periods(Factor A), between the three sessions(Factor B), or the interaction between thefactors (A x B), (P>.20 in all cases).

Paired 't' test: The J-IR during the 'test'periods of both MOM and COM sessions wassignificantly lower than that of thecorresponding 'pre' period, by an average of3.4 bpm and 1.5 bpm, respectively (P<.05 inbot.h cases). The HR remained significantlylow after COM (P<.05). There was also asignificant decrease in RR in the 'test'periods of both MOM and COM sessions (byan average of 2.6 cpm and 4.7 cpm,respectively, P<.OOl, in both cases, comparedt.o the corresponding preceding period). Thiseffect persisted during the 'post' periods ofboth MOM and COM sessions (a decrease of

Indian J Physiol Pharmacal 1998; 42(1)

2.0 cpm and 1.8 cpm respectively, P<.05compared to the corresponding precedingperiod).

There was a significant decrease in skinresistance level (SRL) during the 'test' periodof the MOM session, compared to thepreceding period (P<.Ol). There was also asignificant decrease in SRL in the 'post'period of the MOM session compared to 'pre'(P<.OlJ.

There was no difference in the trend ofresults according to the order of the threesessions (MOM, COM, NT) though the smallsample size (four subjects with eachsequence) precluded using statisticalanalysis.

DISCUSSION

The present study has shown that mentalrepetition of a syllable either meaningful(MOM) or neutral (COM), causes a decreasein heart and breath rate. Non targetedthinking (NT) for the same period of timedoes not have a similar effect. This ,'csllit issimilar to reports about the physiologicalchanges during Transcendental Meditation(TM) (8,9). During the practice of TMsubjects silentlx repeat a particularman tram (see below) throughout each 20 minsession, returning focus to it wheneverattention wanders (10). A unique mantramis assigned to each individual, with the ideathat a particular sound resonates optimallywith a specific nervous system. Themantram is not 'meaningful' in the senseused in the present study.

It was noted that the change which wasunique to the repetition of the meaningful

Autonomic Changes while Repeating Syllables 61

syllable ('OM'), during MOl\'l sessions was asignificant decrease in the skin resistancelevel (SRL). This change is opposite to thatobserved in the studies on TM by (8,9), inwhich an increase in skin resistance wasreported.

It is now well recognized that differentsubdivisions of the sympathetic nervoussystem need not always be activatedsimultaneously. The responses to a givenstimulus vary, depending on the individualand on the stimulus (11). Hence a subjectmay have a reduction in HR (reduced cardiacsympathetic tone) at the same time as adecrease in skin resistance level (SRL),which is believed to be due to increasedsudomotor sympathetic tone. Theinterpretation of change in skin resist.anceis open to continuing debate. The sweatglands are believed to be the majorcontributors to changes in the spontaneouselectrodermal activity (EDA) as is observedby recording the SRL (12). Human sweatglands are generally known to receivepredominantly sympathetic cholinergicinnervation (13). Hence though the EDA isregulated by the sympathetic nervoussystem. the EOA and cardiac sympatheticcontrol systems are recognized to beorganized differently (14). The HR isbelieved to be influenced by somatic activityand movement control mechanisms, whereasthe EDA appears to be determined primarilyby motivational or attentional arousal.Hence mental repetition of both 'OM' and'one' may reduce somatic activity (HRreduction), while the mental repetition of'OM' appears to cause an increase inattentional arousal (reduced SRL), as well.

In addition to the conventional conceptof an increase in skin resistance signifying

62 Telles et al

an increase in sympathetic tone, thesensitivity of the skin resistance (response)to significant stimuli is well known (the 'liedetection test').

It was reported (15) that the generationof frequent and large electrodermal skinresponses were the only indication that inprosopagnosic patients, who have lost theirability to recognize faces, the process ofrecognition is still taking place. It was alsonoted that in these patients the results ofcognizance were not available toconsciousness. While these findings cannotbe directly applied to the present results,they may suggest that even though mentalrepetition of both 'OM' and 'one' causecomparable changes in HR and RR, theneural processes involved in recognizing thesignificance of the syllable 'OM' are active,as renected by the decrease in SRL.

Previous studies have demonstrated thatsubjects with a short experience ofmeditation (comparable to the subjects of thepresent study), show similar inhibition insensory neural processing at mesencephalicand diencephalic levels, while repeating both'OM' and 'one' (1). In the same study, inexperienced meditators neural processing atthese levels was significantly facilitatedwhile repeating 'OM'. These observation onsensory neural processing, were based onrecordings of middle latency auditory evokedpotentials. In both short duration andexperienced meditators there weresignificant changes (in opposite directions)in the amplitude of the Na wave. This is anegative wave occurring betwen 14-18 msecafter the stimulus, with a neural generatorat mesencephalic/diencephalic level (16). An

Indian J Physiol Pharmacol 1998; 42(1)

increase in peak amplitude observed inexperienced meditators, suggests facilitionof sensory neural processing (17). In aseparate study (2) on the autonomic changesin experienced 'OM' meditators, there wasno change in the skin resistance level whilerepeating 'OM'. This is in contrast to theshort duration meditators of the presentstudy.

Hence to sum up the results of thepresent and previous studies, 0) a decreasein HR, RR (conventional indicators ofrelaxation) follow the mental repetition ofany syllable, (ii) subjects who have brief (20days) experience of medication on ameaningful syllable ('OM'), show asignificant decrease in SRL during repetitionof that syllable, but not while repeating aneutral syllable or during non targetedthinking. Subjects with longer meditationexperience do not show this change, (iii)experienced meditators show significantfacilitation of sensory neural processing atmesencephalic/diencephalic levels whilerepeating the syllable on which theymeditate. NaiVe meditators do not show thischange. These results suggest that theprocess of understanding the significance ofa meaningful syllable may be continuous,and is significantly influenced by theduration of meditation. The decrease in SRLwas observed in naive meditators but not inexperienced meditators, hence this changemay represent an intermittent stage duringwhich changes in sensory evoked potentials(EPs) arc not yet obtained. The presentresults also support the idea that the SRLmay indicate cognitive involvement in theobject of meditation in addition to being aconventional indicator of sympathetic tone.

Indian J Physiol Pharmacol 1998; 42(1) Autonomic Changes while Repeating Syllables 63

REFERENCES

TelleJ S. Nagarathna R, Nagendra HR, DeJiraju T.AlterationJ in auditory middle latency evokedpotentials during meditation on a meaningfulsyllable - 'OM'. Intern J Neurolci 1994; 76: 87-93.

2 Telles S, Nagarathna R, Nagendra HR. Autonomicchanges during 'OM' meditation. IndIan J PhysiolPharmacol 1995; 39 (4): 418-420.

3. Dehus W, Kellerova E Reaction of arterial andvenOUJ vessels in the human forearm and hand todeep breath or mental Jtrnin. Gill! SCI 1971; 40:271-282.

4. Jasper III-I. The ten·twenty electrode system of theInternational Federation. [o.'/ectroenceph ClillNtllrophysioll958; 10: 371-375.

5. Rechtschaffen A, Kales A. A manual of standardizedterminology, techniques and Icoring Jyltem of sleepJtates of human subject:s. WaJhington DC, PublicHealth Service, Government Printing Office, 1968.

6. Roy M, Steptoe A The inhibition of cardiovascularresponseJ to mental UreSJ following aerobicexercise. Pllychophy.iol 1991; 28: 689-699.

7. Zat Jtl. Biostatistical Analy.i•. Second Edition.London, Prentice-Hall, 1984.

8. Wallace RK. Physiological effects of transcendentalmeditation. Science 1970; 167: 1751-1754.

9 Wallace RK, Benson 1-1, Wil5Qn AF. A wakefulhypometabollc physiologic state. Am J Physioll971;21: 795-799.

10. Woolfolk RL. Psychophysiological correlate. ofmeditation. Arch Gen Pllychiol 1975; 32: 1326-1333.

11. Engel BT. Stimuhl' retpon.e and indi"idualre.ponu .pecificity. Arch Cen Pllychiat 1960; 2:305-313.

12. Fowlet DC. The eccrine system and electrodermalactivity. In Coles MGH, Donch;n E, Porget SW, eds.,P.ychophysiology; .y.tems, procene. andapplication., New York, Guilford Pre.. 1986: 51­gO.

13. Shield. SA, MacDowell KA, fo'airchild SB, CampbellML. Is mediation of sweating cholinergic,adrenergic or both? A comment on the literature.P~ychIJ/)hysjfJl 1987; 24: 312-319.

14. Roberts LE. Comparative psychophysiology of theelectrodermal and cardiac control 'ylltems. InObrisl PA, Black AU, Brener J, Dicata LV, eds.Cardiovascular psychophy.iology: current issues inre.ponse mechani.ms, biofeedback andmethodology. Chicago, Aldine Press, 1974: 163-189.

15. Tranel D, Damuio AR. Knowledge withoutawarene..; an autonomic index of facial recognitionby pro.opagnosic•. Science 1985; 228: 1453-1454.

16. Deiber MP, IbaneJ: V, Fi.her C, Perrin F, MauguiereF. Sequential mapping favour. the hypothesis ofdi.tlnct generators for Na and Pa middle latencyauditory evoked potential!. Electroenceph ClinNeurophyllol 1988; 71: 187-197.

17 Woods DL, Clayworth CC. Click spalial positioninfluences middle latency auditory evoked potential(MAEP.) in human.. Efecroetlceph CllnNeurophyliol 1985; 60: 122-129.