THE EFFECT OF MOTIVATIONAL INSTRUCTIONS ON P300
AMPLITUDE
Au ho s: M.T. Ca illo-de-la-Peña, F. Cada ei a
This is he pee e iewed e sion o he ollowing a icle: Ca illo-de-la-Peña M.T.; Cada ei a,
F. (2000). The e ec o mo i a ional ins uc ions on P300 ampli ude. Neu ophysiologie Clinique
/ Clinical Neu ophysiology, 30, 232-239. doi: 10.1016/s0987-7053(00)00220-3
This a icle may be used o non-comme cial pu poses in acco dance wi h Else ie Masson,
Else ie and Socié é de Neu ophysiologie Clinique de Langue F ançaise e ms and condi ions
o use o sel -a chi ed e sions.
Pos -p in ( inal d a pos - e e eeing)
2
The e ec o mo i a ional ins uc ions on P300 ampli ude
Au ho s: M.T. Ca illo-de-la-Peña, F. Cada ei a
Depa men o Clinical Psychology and Psychobiology, Uni e si y o San iago de Compos ela,
15705 San iago de Compos ela, Spain
Pos -p in ( inal d a pos - e e eeing)
3
Summa y – The aim o his in es iga ion was o de e mine he e ec on P300 ampli ude o
ins uc ions aimed a inc easing he subjec ’s deg ee o ask in ol emen . To his end, wo
di e en s udies we e ca ied ou . In S udy 1, 20 uni e si y s uden s we e es ed wi h an audi o y
e en - ela ed po en ial (ERP) oddball pa adigm ( a ge : 1 100 Hz; s anda d: 1 000 Hz) in wo
consecu i e uns, each wi h a di e en se o ins uc ions; a e he i s un, subjec s we e e bally
mo i a ed o inc ease hei le el o pe o mance in he second un. In S udy 2 (pe o med 1 yea
la e ), ERPs we e simila ly ob ained om he same subjec s du ing wo oddball uns, bu his ime
bo h es s we e p eceded by neu al ins uc ions. The ampli ude and la ency o N1 and P2 elici ed
by non- a ge s and o N2 and P3 in a ge wa e o ms we e e alua ed. The indings showed ha
ollowing mo i a ing ins uc ions, P3 ampli ude inc eased whileP3 la ency showed a non-
signi ican dec ease. The ampli ude o P2 o non- a ge s imuli - which could be in e p e ed as
P250 - was also a ec ed by he ins uc ions p o ided. The o e all esul s sugges ha he
p esen a ion o mo i a ing ins uc ions is ollowed by a highe amoun o a en ional esou ces
alloca ed o all s imuli, and a mo e e icien e alua ion and disc imina ion o ele an a ge s. The
implica ion o hese indings o he clinical use o P300 has been discussed. © 2000 Édi ions
scien i iques e médicales Else ie SAS
P300 / ERP / mo i a ion / clinical applica ion / ask in ol emen
Résumé – E e des ins uc ions mo i an es su l’ampli ude du P300. L’objec i de ce a ail
é ai d’é udie l’e e su l’ampli ude du P300 des ins uc ions données aux suje s pou augmen e
leu mo i a ion lo s de la éalisa ion d’un pa adigme oddball. Pou cela, nous a ons éalisé deux
é udes di é en es. Dans l’é ude 1, une âche oddball audi i e (cible : 1 100 Hz ; équence : 1 000
Hz) a é é p ésen ée à 20 é udian s ; ap ès une p emiè e sé ie s anda d, les suje s on eçu des
ins uc ions isan à augmen e leu deg é de mo i a ion dans la deuxième sé ie. Dans l’é ude 2,
éalisée un an plus a d, les pe o mances des mêmes suje s on é é en egis ées pendan la
éalisa ion de deux sé ies oddball, ou es les deux p écedées d’ins uc ions s anda ds. L’ampli ude
e la la ence du N1 e du P2 ob enues en éponse aux sons équen s e l’ampli ude e la la ence
du N2 e du P3 aux s imuli cibles on é é é udiées. Dans la sé ie p écédée des ins uc ions
mo i an es, l’ampli ude du P3 é ai augmen ée ; sa la ence é ai accou cie mais de açon non
signi ica i e. L’ampli ude du P2 aux équences – aussi in e p e é comme le P250 – é ai
égalemen modi iée pa les ins uc ions. Les ésul a s de ce e é ude suggè en que la p ésen a ion
d’ins uc ions mo i an es en aine une é alua ion e une disc imina ion des s imuli signi ica i s
plus e icace ; celai semblan e lè e une plus g ande quan i é de esou ces a en ionnelles
allouées à ous les s imuli. Les implica ions de ces ésul a s pou l’applica ion clinique du P3 son
discu ées. © 2000 Édi ions scien i iques e médicales Else ie SAS
P300 / ERP / mo i a ion / applica ion clinique
Pos -p in ( inal d a pos - e e eeing)
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The P300 componen o e en - ela ed po en ials (ERPs) has been ex ensi ely in es iga ed in
clinical p ac ice as i p o ides an easily ob ained, nonin asi e index o gene al cogni i e
unc ioning. Longe P3 la encies, ela ed o an inc eased delay in s imulus classi ica ion in a
disc imina ion ask, ha e been ound in elde ly subjec s [16, 24], and in pa ien s wi h demen ia
[1, 10], ea ly Alzheime ’s disease [26] o in cases o alcoholism [4, 42], among o he s. A dec ease
in P3 ampli ude has also been clinically obse ed in dep essi e [3], schizoph enic [13] and
alcoholic subjec s [28], and has been iden i ied as a isk ma ke o alcoholism o he de elopmen
o a psychopa hology [27, 30, 32, 33, 35].
The clinical use o P3 has been based on a la ge numbe o s udies on he basic pa ame e s ha
in luence i s ampli ude and la ency [20]. Johnson sys ema ized his ield o esea ch and p oposed
a 3-componen model, namely, subjec i e p obabili y, s imulus meaning, and ansmission o
in o ma ion [14]. Ne e heless, esea ch has been mainly ocused on ask- ela ed a iables, and
e y ew s udies ha e in es iga ed he e ec o o he non-speci ic ac o s p esen a he ime o
eco ding ha may ha e a decisi e in luence on P3 indices. Fo ins ance, Johnson [14] s a ed ha
he ‘s imulus meaning’ dimension is de ined by ask complexi y, s imulus complexi y and
s imulus alue, and ha his la e a iable is mainly de e mined by he amoun o ewa d
associa ed wi h he disc imina ion o s imuli. Ne e heless, in his model li le a en ion was gi en
o he subjec ’s posi i e disposi ion o mo i a ion o e icien ly pe o m a disc imina ion ask such
as he oddball pa adigm, a a iable which may de e mine he subjec i e meaning o he ask. This
ask-in ol emen ac o may be c ucial in a clinical se ing, aking in o accoun he ac ha
pa ien s a e qui e o en unwilling o pa icipa e in he eco ding p ocess o ind i di icul o
pe o m he equi ed asks. The ele ance o ask in ol emen in speci ic se ings has been
illus a ed by Lau en e al. [17], who poin ed ou ha one o he me hodological di icul ies in
s udying he P300 componen in schizoph enic pa ien s was o ob ain adequa e pa ien -con ol
ma ching o mo i a ion. In ac , ‘mo i a ion’ has o en been used as an explana o y ac o o
a ia ions in P300 pa ame e s in schizoph enic [19, 36, 40] and dep essi e pa ien s [5], subjec s
wi h mig aine [7], o he elde ly [41]. Polich and Kok ha e also sugges ed ha o he non-speci ic
ac o s such as a ousal may a ec P3 ampli ude [25]
Al hough se e al s udies ha e indica ed ha he educ ion in P300 ampli ude in some clinical
g oups may be due o a mo i a ional de ici , he e ec o mo i a ion on he P3 componen has no
been sys ema ically add essed in he li e a u e. The exis ing esea ch has ocused on he incen i e
alue o he s imuli, which seems o a ec P3 ampli ude bu no i s la ency. La ge ampli udes
ha e been ound when he mone a y alue o he a ge is inc eased [2, 12] o when i is used as
a eedback s imulus (i.e. when i signi ies a co ec pe o mance, a he han when i is simply
coun ed) [14]. The e ec o an incen i e on P3 ampli ude has also been examined in clinical and
con ol g oups. I has been ound ha alcoholics o subjec s wi h a amily his o y o alcoholism
did no show la ge P300 ampli udes o he a ge whe he i implied ewa d o loss o ewa d [29,
31].
Gi en he po en ial ele ance o mo i a ion on ERP pa ame e s, in he p esen s udy we a emp ed
o analyze he e ec o his a iable using a di e en s a egy. The aim was o de e mine o wha
ex en he subjec ’s deg ee o ask in ol emen , in luenced by he ins uc ions p o ided, migh
a ec he P3 componen . To his end, he ERPs we e eco ded in wo consecu i e se ies while
subjec s pe o med an oddball ask consis ing o disc imina ion be ween 1 000 Hz (s anda d
Pos -p in ( inal d a pos - e e eeing)
5
s imulus) and 1 100 Hz ( a ge s imulus) ones. The i s un in S udy 1 was p eceded by neu al
ins uc ions, and he second by ins uc ions aimed a mo i a ing he subjec s and inc easing hei
le el o p o iciency in he pe o mance o he ask. To ake in o accoun he possible e ec s o
p ac ice o habi ua ion on he P3, in wo epea ed occasions, in a simila s udy he same subjec s
pe o med wo consecu i e oddball asks bu only ecei ed neu al ins uc ions, and no
mo i a ing ins uc ions be o e he second un (S udy 2). This wo k is pa o a longi udinal
esea ch p ojec aimed a s anda dizing he eco ding p o ocols o uni e si y s uden s, and in his
con ex he eco dings o S udy 1 and S udy 2 we e he e o e sepa a ed by an ex ended pe iod (1
yea ). I was expec ed ha he p esence o mo i a ing ins uc ions (S udy 1, second un) would
inc ease he amoun o a en ional esou ces alloca ed o he ask, and consequen ly p oduce an
enhancemen o P300 ampli ude.
Ma e ials and me hods
Subjec s
Twen y uni e si y s uden s (8 males, 12 emales) aged be ween 18–23 yea s (mean age: 19 yea s,
SD: 1.37 yea s) con ac ed o e wo consecu i e yea s we e included in he s udy. All subjec s
we e in good heal h and had no his o y o neu ological o psychia ic diso de , o d ug abuse.
S imuli and p ocedu e Subjec s we e exposed o pu e- one beeps o 50 ms du a ion (10 ms ise
and all) and 60 dB SPL by means o ea phones. The in e s imulus in e al (ISI) was 1 500 ± 100
ms, and he in e al be ween uns was app oxima ely 2 min. Subjec s had o de ec he a ge s (1
100 Hz) inse ed andomly be ween s anda d (1 000 Hz) ones, and p ess a bu on wi h he
dominan hand when he a ge s appea ed. Each un consis ed o a sequence o 200 s imuli, wi h
a global p obabili y o a ge s o 0.20. In S udy 1, subjec s pe o med wo consecu i e oddball
asks wi h di e en ins uc ions o each. The i s se ies was p eceded by he ollowing
ins uc ions: “Now you will hea wo ypes o one; some o hem a e high-pi ched (‘bip’) while
he o he s, which a e mo e equen , a e low-pi ched (‘bop’). Whene e you hea a ‘bip’ you mus
p ess his bu on as as as possible. Please y o a oid unecessa y mo emen s o blinking du ing
he es ”. A e a 2-minu e es pe iod, a second se ies was p esen ed wi h he ollowing
ins uc ions: “Now you ha e o accomplish he same ask as be o e,bu his ime i is pa icula ly
impo an ha you do well. We a e eco ding you pe o mance on he compu e , and you da a
will be compa ed wi h he class oom s anda ds. Remembe ha i is impo an o a oid unecessa y
mo emen s o blinking du ing he es ”. S udy 2 was ca ied ou 1 yea la e . Subjec s again
pe o med wo consecu i e oddball asks, bu his ime bo h we e p eceded by he same neu al
ins uc ions as in he i s un o S udy 1.
ERP eco dings
Fo his in es iga ion, EEG ac i i y was eco ded wi h in elec odes a Fz, Cz and Pz elec ode
si es, e e enced o he nose. An elec ode placed on he o ehead se ed as g ound. Addi ional
elec odes placed abo e and below he le eye we e used o moni o ocula a i ac s.
EEG ac i i y was il e ed wi h a bandpass o 0.1–30 Hz (24 dB/oc a e ollo ) and ampli ied 20
k. Elec ode/skin impedance was kep below 5 kΩ. Signals we e sampled con inuously a a a e
o 500 Hz. The signal was p ocessed o -line: i s he EEG was co ec ed o e ical ocula
mo emen s, using he algo i hm de eloped by Semli sch e al. [34], and hen he EEG was
epoched om 100 ms p e-s imulus o 900 ms pos -s imulus. Linea ends we e elimina ed, he
signal was adjus ed o 0 μV p e-s imulus baseline and il e ed wi h a digi al il e (0.1–30 Hz).

Pos -p in ( inal d a pos - e e eeing)
6
T ials a ec ed by elec omyog aphic ac i i y o o he a i ac s (± 90 μV) we e iden i ied by isual
inspec ion and hen ejec ed.
Da a analysis
In each s udy, a e age ERPs we e compu ed sepa a ely a Fz, Cz and Pz o each un (1s /2nd)
and s imulus ca ego y ( a ge /non- a ge ). The a e aged ERPs we e analyzed wi h a semi-
au oma ic peak de ec ion p og am, using a compu e algo i hm which sea ched o he
maximum/minimum peak ampli ude wi hin p ede ined la ency windows. Peaks we e hen
e i ied and adjus ed by isual inspec ion. Ampli ude and la ency alues we e au oma ically
ans e ed o an ASCII ile o subsequen analysis.
The peaks iden i ied we e N1 (75–150 ms) and P2 (150–250 ms) o he wa e o ms elici ed by
s anda ds, and N2 (200–300 ms) and P3 (275–450 ms) o hose elici ed by a ge s.
Da a we e analyzed wi h a epea ed measu es analysis o a iance (ANOVA) using s udy (1s
e sus 2ndyea ), un (2 uns) and elec ode si es (3 si es) as wi h in subjec ac o s. Sepa a e
analyses we e ca ied ou o each componen la ency and ampli ude. Signi ican le els we e
de e mined using deg ees o eedom adjus ed by he G eenhouse-Geisse co ec ion when
di e gence om he assump ion o sphe ici y was ound o be signi ican [39]. Signi ican e ec s
we e examined wi h pai ed - es s.
Resul s
The o e all a e ages o ERPs a Fz, Cz and Pz ob ained om non- a ge and a ge s imuli in he
i s and second s udies ha e been shown in igu es 1 and 2, espec i ely. The wa e o ms eco ded
in he i s and second uns a e supe imposed. Visual inspec ion o he wa es shows an inc ease
in P3 ampli ude o a ge s in he second un, bu only in S udy 1. As can be seen in igu e 2, he
wa e o ms ob ained in he i s and second uns o S udy 2 p esen ed a ma ked deg ee o o e lap.
Repea ed measu es ANOVA showed a signi ican s udy × un in e ac ion on P3 ampli ude o
a ge s (F[1, 19] = 4.74; P = 0.04). This e ec was independen o elec ode posi ioning. As can
be seen in able I, he p esen a ion o mo i a ing ins uc ions in he second un o S udy 1
p o oked highe ampli udes a all he elec ode si es. This P300 inc ease in he second un was
no obse ed in S udy 2 ( able II).
Fo P2 ampli ude o equen s imuli, signi ican main e ec s we e ound o s udy (F [1, 18] =
5.18; P = 0.035) and un (F [1, 18] = 4.55; P = 0.047), as well as a e y signi ican s udy × un ×
elec ode in e ac ion (F [2, 36] = 6.96; P = 0.006; ε = 0.78). A pai ed - es e ealed highe P2
ampli udes in he second un, bu only in S udy 1 and o Cz and Pz.
Rega ding la ency alues, signi ican ly sho e N2 la encies we e ound in he second un in bo h
s udies (F [1, 16] = 5.61; P = 0.029 o he un e ec ). Fo P3 la ency, he e was a non-signi ican
end owa d sho e la encies in he second mo i a ed un o S udy 1 o Fz and Cz (F [2, 38] =
3.20; P = 0.067; ε = 0.78 o he s udy × un × elec ode in e ac ion). No o he e ec o in e ac ion
was ound o be signi ican o o he la ency o ampli ude pa ame e s.
To u he cla i y he e ec o mo i a ing ins uc ions ound in S udy 1, he beha io al esponses
o a ge s in he i s and second uns we e addi ionally analyzed. In he i s se ies, he mean
unning ime (RT) was 457.99 ms (mean SD = 104.73 ms) wi h a 90% co ec sco e, and in he
Pos -p in ( inal d a pos - e e eeing)
7
second se ies he mean RT was 406.80 ms (mean SD = 93.22 ms) wi h a 93.88% co ec sco e.
Pai ed - es s e ealed a signi ican di e ence be ween bo h uns in he mean RT ( wo- ailed -
es , = 2.92; P = 0.009).
Discussion
The esul s ob ained he e show ha he ERP P3 componen is a ec ed by non-speci ic ac o s
such as he mo i a ion o pe o m a ask co ec ly. P o iding ins uc ions aimed a inc easing he
subjec ’s deg ee o in ol emen in he ask seemed o esul in a mo e e icien p ocess o
e alua ion and decision-making ega ding ele an s imuli, mani es ed bo h a he
neu ophysiological and beha io al le el. An inc ease in P3 ampli ude and a end owa ds a
dec ease in P3 la ency ook place when an oddball ask was p eceded by mo i a ing ins uc ions.
The possibili y o he inc ease in P3 ampli ude in he mo i a ed se ies being due o he acili a ing
e ec o epe i ion was uled ou by S udy 2.
When bo h disc imina ion asks we e p eceded by he same neu al ins uc ions, no signi ican
e ec s o un eme ged. Unde he mo i a ed condi ion, howe e , he subjec ’s beha io al
pe o mance was also signi ican ly imp o ed: al hough he esponses we e simila ly accu a e, he
RT became signi ican ly educed when subjec s we e mo i a ed.
A possible explana ion o his s udy g oup’s mo e e icien s imulus e alua ion and
disc imina ion unde mo i a ed condi ions may be ha , wi h a highe deg ee o ask-in ol emen ,
subjec s we e mo e able o concen a e on a ge s imuli and o block ou he i ele an in o ma ion
om non- a ge s. Howe e , his hypo hesis is con adic ed by he highe P2 ampli udes o non-
a ge s imuli, which we e also ound in he mo i a ed se ies. P2 ampli ude o equen s imuli
(also called ‘P250’ by some au ho s [9]) has been conside ed an index o he amoun o cen al
p ocessing o non ele an s imuli du ing disc imina ion asks [6, 9].
Thus, a hypo hesis which is mo e consis en wi h ou da a could be ha he e iciency in
p ocessing was de e mined by a highe deg ee o a en ional esou ces alloca ed o all s imuli,
e en o non- a ge s, when subjec s had been p o ided wi h mo i a ing ins uc ions.
This inc ease in p ocessing abili y may ha e been ela ed o an inc ease in he le el o gene al
a ousal o awa eness induced by he ins uc ions. This in e p e a ion is, howe e , ques ioned by
he ac ha N1 ampli ude, which one would expec o a y wi h di e en deg ees o awa eness
[38], did no di e be ween s udy condi ions. Ne e heless, as P3 ampli ude is sensi i e o
changes in a ousal [25], he possibili y ha he mo i a ing ins uc ions p oduced inc easing
a ousal, which in u n inc eased he P3 ampli ude, canno be comple ely uled ou .
Mo i a ing ins uc ions p oduced a sho ening o RTs wi hou a signi ican change in P3 la ency.
This dissocia ion be ween P3 la ency and RTs, also p e iously epo ed in he li e a u e [18], may
be unde s ood by aking in o accoun he na u e o he ask and he ins uc ions p o ided. Since
subjec s we e al eady e y accu a e in he i s se ies (90% co ec sco e), i is possible ha he
mo i a ing ins uc ions p i ileged a speed s a egy in he second se ies. Consequen ly, and gi en
he ac ha he ask equi emen was exac ly he same in bo h se ies, he ins uc ions p obably
induced quicke esponses wi hou signi ican ly changing he s imulus e alua ion ime.
P e e baum e al. also ound ha speed ins uc ions had a s onge e ec on RTs han on P3
la ency [23]. The inc eased a ousal due o ecei ing mo i a ing ins uc ions may also con ibu e
Pos -p in ( inal d a pos - e e eeing)
8
o explaining he inc ease in esponse speed. As Hackley and Valle-Inclán ha e demons a ed,
ansien changes in a ousal p oduced by a non- ele an accesso y one educed he RTs [11].
Thus, ins uc ions aimed a e ec i ely mo i a ing he subjec p oduced an inc ease in P3
ampli ude, which may be in e p e ed in he ligh o he ia chic model p oposed by Johnson [14].
Mo i a ion o ask in ol emen is a non-speci ic ac o ha may inc ease s imulus alue, one o
he ac o s in Johnson’s equa ion. I seems as i all he s imuli become mo e ele an when
subjec s a e mo i a ed in spi e o ha ask di icul y, and s imulus p obabili y keep cons an . A
a physiological le el, he changes in ERPs induced by mo i a ing ins uc ions may be in e p e ed
as he esul o an inc ease in he ac i i y o he no ad ene gic sys em. Pineda e al. ha e
demons a ed he ole o his sys em on he gene a ion and modula ion o P3 ampli ude in
monkeys, and ound a signi ican educ ion in P3 ampli ude a e he adminis a ion o ad ene gic
alpha an agonis s, o ha had been caused by lesions o he locus coe uleus and i s ascending
ibe s [21, 22]. Thus, i appea s ha he inc ease in he amoun o a en ional esou ces alloca ed
o a ask in mo i a ed condi ions could be associa ed wi h an inc ease in he ac i i y o he
no ad ene gic sys em, and consequen ly, wi h an inc ease in P3 ampli ude.
The abo e esul s may ha e some ele ance o he in e p e a ion o P3 ampli ude as a clinical
index, a leas a g oup le el. I is possible ha he educ ion o P3 ampli ude in pa ien g oups
may be due o a mo i a ional de ici . This mo i a ional de ici has been ound in alcoholics, whose
P3 ampli udes do no seem o espond o he p esen a ion o ewa ds associa ed wi h he
disc imina ion ask [29]. I has also been ound ha eedback aining ega ding a ask p oduced
an enhancemen o P3 ampli ude in schizoph enics, especially in hose which p esen ed a mo e
de ined educ ion in P3 ampli ude [8]. Also, P300 ampli ude has been nega i e and signi ican ly
ela ed o a s a e o despai and suicidal isk in a sample o dep essi e pa ien s [37]. Ne e heless,
he con ibu ion o mo i a ion o di e ences in P300 be ween pa ien s and con ols is no clea .
Kemne e al. [15] did no ag ee wi h he iew ha P300 abno mali ies in hype ac i e child en
wi h a en ion de ici we e seconda y o an impai men in mo i a ion. They ound ha hese
child en p esen ed signi ican educ ions in P3 ampli ude o di e se s imuli, i espec i e o ask
ele ance.
In summa y, his s udy unde lines he impo ance o mo i a ion o ask in ol emen in
de e mining P3 ampli ude and i s in e p e a ion o clinical pu poses. ‘Dynamogenic’ ac o s such
as mo i a ion o emo ion should be ully in es iga ed in o de o de e mine he e al na u e o he
educ ion in P3 ampli ude in a numbe o psychopa hologies. The p esen wo k p o ides a simple
expe imen al assessmen o ask in ol emen which p oduces a signi ican inc ease in P3
ampli ude, which could be easily adop ed in speci ic se ings. Ne e heless, i could be a gued
ha he ins uc ions p o ided in he p esen s udy may ha e had o he consequences, such as
aising he le el o anxie y, which in u n may ha e in luenced P3 pa ame e s. Thus i is ad isable
ha u u e s udies include o he kinds o ewa d (i.e., mone a y) o es whe he he P3 componen
in di e en clinical g oups is sensi i e o he manipula ion o mo i a ional le els.
Pos -p in ( inal d a pos - e e eeing)
9
Re e ences
1.
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