8. ANÁLISIS DE LOS RESULTADOS
8.3 CUERPOS EN TRANSITOS
R ew ard is the p o s itiv e subjective e ffe ct o f a stim ulus, w h ic h is ehcited by ‘n a tu ra l’ stim uh in the e n v iro n m e n t, such as those associated w ith survival, such as fo o d , w ater and sexual contact. H o w e v e r, drugs th a t are abused by m an b rin g a b o u t the same e m o tio n a l and
Chapter one Introduction
n euroche m ical responses elicited b y natu ra l rewards. A d m in is tra tio n o f these drugs gives rise to subjective feelings o f pleasure and w ell-being. Indeed, it is the desire to elevate m o o d and achieve a ‘h ig h ’ th a t o fte n m otivates in itia l d ru g use. H o w e v e r, add ictive drugs are n o t o n ly rew arding, b u t they are also re in fo rc in g , in th a t they stim ulate the user to repeat the behaviours associated w ith th e m (W h ite 1996). T h e y th e re fo re stim ulate a user to seek and take the d ru g again. In vulnerable people, the repeated a d rn in istra tio n o f an ad dictive d ru g can b rin g a b o u t changes in the b ra in th a t p ro m o te c o n tin u e d d ru g taking, w h ic h subsequently becomes progressively harder to c o n tro l. T h is co m p u lsive use o f drugs can eventua lly becom e o u t o f c o n tro l, fo rc in g the Life o f the user to becom e progressively focused o n o b ta in in g , using and re co ve rin g fro m the effects o f drugs, despite th e ir serious negative consequences (O 'B rie n & M c L e lla n 1996). O n ce such an a d d ic tio n has taken h o ld , it tends to fo llo w a c h ro n ic course; even a fte r lo n g periods o f abstinence, and perhaps o ve r a life tim e , d ru g addicts fin d th a t a re tu rn o r relapse to active d ru g use can easily be p recipitated . A d d ic tio n is th e re fo re a c h ro n ic, relapsing m e d ica l illness, whose p a th o p h y s io lo g y is characterised by co m p le x and lo n g -la stin g m olecular, cellular and system -level changes in the b ra in (G o ld ste in 1994).
T h e repeated a d m in is tra tio n o f drugs o f abuse n o t o n ly brings a b o u t co m p u lsive use, b u t also tolerance, sensitisation and dependence. Tolerance is the decrease in the effects o f a d ru g despite a co nstant dose, w h ic h is o fte n m anifest in the need fo r a larger dose to be adm inistered to m a in ta in the same e ffe c t (M endelson
et a l
1998). I n term s o f h u m a n drug abuse, tolerance o fte n develops to a d ru g ’s re w a rd in g o r pleasurable effects, encouraging the user to increase th e ir ingested dose, w h ic h exacerbates the changes th a t are o c c u rrin g in the b ra in to b rin g ab o u t ad d ictio n . Sensitisation o f a d ru g ’s effects can also occur: in h u m a n addicts, cra vin g o f o r desire fo r a d ru g m ay u ndergo such an enhancem ent (R o b in so n & B erridge 1993). B o th tolerance and sensitisation can exist in the same in d iv id u a l: h o w ever, the tw o pheno m e na o ccu r to d iffe re n t aspects o f a d ru g ’s effects, such as re w a rd o r ‘Hking’, w h ic h tends to becom e to le ra n t, and cra vin g o r ‘w a n tin g ’, w h ic h tends to sensitise. D ependence refers to the p h e n o m e n o n w hereby, u p o n d ru g cessation, co g n itive , e m o tio n a l o r physical w ith d ra w a l sym ptom s are experienced, and is m ediated by the a dapta tion o f cells, circuits o r organ systems in response to d ru g a d m in is tra tio n (G o ld s te in 1994).Chapter one Introduction
E a rly psycholog ical theories o f d ru g a d d ic tio n assumed the avoidance o f the aversive properties o f d ru g w ith d ra w a l was the p rim a ry m o tiv a tio n fo r co m p u lsive d ru g in g e stio n in addicts (see Lyvers 1998; W ise 1987). H o w e ve r, the a lle via tio n o f w ith d ra w a l sym ptom s ca n n o t exp la in persistent d ru g seeking b e h a vio u r since some drugs o f abuse w h ic h are h ig h ly a d dictive, such as cocaine and am phetam ine, have relative m ild e m o tio n a l w ith d ra w a l sym ptom s, and do n o t p ro d u ce physical w ith d ra w a l (G a w in 1991). M o re o ve r, the d is c o m fo rt associated w ith w ith d ra w a l ca n n o t be the m a jo r obstacle to recovery, since addicts o fte n relapse to d ru g -ta kin g b e h a vio u r lo n g a fte r w ith d ra w a l sym ptom s have dissipated, even fo r drugs w ith severe physical w ith d ra w a l sym ptom s such as h e ro in and a lc o h o l (O 'B rie n
el al.
1992). F u rth e rm o re , pleasure-seeking alone c a n n o t explain the persistence o f d ru g -ta k in g b e h a vio u r in addicts: the re w a rd in g p ro p e rtie s o f drugs o fte n habituate w ith repeated a d m in istra tio n , as is o fte n seen in alcoholics, fo r w h o m a lco h o l no lo n g e r brings pleasure b u t o fte n elicits feelings o f depression (Weiss & P o rrin o 2002), and in cocaine addicts, in w h o m the ‘h ig h ’ is reduced fo llo w in g repeated d ru g a d m in istra tio n(V o lk o w
et at.
1997b).A d d ic tio n is n o w u n d e rsto o d to be a m o re co m p le x p h e n o m e n o n th a n the m aintenance o f h e d o n ic hom eostasis: drugs o f abuse seem to b rin g a b o u t a sensitisation o f the b ra in systems th a t are in v o lv e d in in ce n tive m o tiv a tio n (R o b in so n & B erridge 1993, 2000). Thus, the ‘w a n tin g ’ o f a d ru g increasingly becomes the d o m in a n t psych o lo g ica l response, at the same tim e as tolerance develops to the rew ard-m ediate d ‘Hking’ o f the drug. These p sych o lo g ica l alterations are extrem ely stable and lo n g lasting, and m ay explain the persistence o f su sce p tib ility to relapse in re co ve rin g addicts, w h ic h is usually the m a jo r obstacle to th e ir re h a b ilita tio n . D ru g -c o n d itio n e d cues are o f p a rtic u la r im p o rta n ce in relapse, and illu stra te the associative learning th a t is believed to u n d e rlie the d e velop m e nt and m aintenance o f addiction : in hum a n addicts, the ris k o f a re tu rn to c ra vin g and drug- seeking b e h a v io u r is elevated u p o n exposure to people, places o r paraphernalia associated w ith p re vio u s d ru g use, suggesting th a t the b ra in stores specific in fo rm a tio n a b o u t drugs and th a t d ru g a d d ic tio n can u ltim a te ly can been view ed as a fo rm o f aberrant association o f drug-associated cues w ith rew a rd o r the sensitised ‘w a n tin g ’ response (C hildress
et al
1986; E h rm a net al
1992; S h iffm a net a l
1996). F u rth e rm o re , the n e u ro ch e m ica l consequences o f d ru g a d m in is tra tio n share a s trik in g n u m b e r o f sim ilarities w ith the processes th a t occur d u rin g associative learning (W h ite 1996). D ru g a d d ic tio n is th e re fo re a consequence o fChapter one Introduction
lo n g -te rm changes in b ra in structure and fu n c tio n , w h ic h can exert fu ll c o n tro l o ve r an a d d ict’ s life.