Not for the Sake of Pleasure Alone

Re­lated: Not for the Sake of Hap­piness (Alone), Value is Frag­ile, Fake Fake Utility Func­tions, You can­not be mis­taken about (not) want­ing to wire­head, Utilons vs. He­dons, Are wire­heads happy?

When some­one tells me that all hu­man ac­tion is mo­ti­vated by the de­sire for plea­sure, or that we can solve the Friendly AI prob­lem by pro­gram­ming a ma­chine su­per­in­tel­li­gence to max­i­mize plea­sure, I use a two-step ar­gu­ment to per­suade them that things are more com­pli­cated than that.

First, I pre­sent them with a vari­a­tion on Noz­ick’s ex­pe­rience ma­chine,1 some­thing like this:

Sup­pose that an ad­vanced team of neu­ro­scien­tists and com­puter sci­en­tists could hook your brain up to a ma­chine that gave you max­i­mal, be­yond-or­gas­mic plea­sure for the rest of an ab­nor­mally long life. Then they will blast you and the plea­sure ma­chine into deep space at near light-speed so that you could never be in­terfered with. Would you let them do this for you?

Most peo­ple say they wouldn’t choose the plea­sure ma­chine. They be­gin to re­al­ize that even though they usu­ally ex­pe­rience plea­sure when they get what they de­sired, they want more than just plea­sure. They also want to visit Costa Rica and have good sex and help their loved ones suc­ceed.

But we can be mis­taken when in­fer­ring our de­sires from such in­tu­itions, so I fol­low this up with some neu­ro­science.

Want­ing and liking

It turns out that the neu­ral path­ways for ‘want­ing’ and ‘lik­ing’ are sep­a­rate, but over­lap quite a bit. This ex­plains why we usu­ally ex­pe­rience plea­sure when we get what we want, and thus are tempted to think that all we de­sire is plea­sure. It also ex­plains why we some­times don’t ex­pe­rience plea­sure when we get what we want, and why we wouldn’t plug in to the plea­sure ma­chine.

How do we know this? We now have ob­jec­tive mea­sures of want­ing and lik­ing (de­sire and plea­sure), and these pro­cesses do not always oc­cur to­gether.

liking expressionsOne ob­jec­tive mea­sure of lik­ing is ‘lik­ing ex­pres­sions.’ Hu­man in­fants, pri­mates, and rats ex­hibit ho­molo­gous fa­cial re­ac­tions to pleas­ant and un­pleas­ant tastes.2 For ex­am­ple, both rats and hu­man in­fants dis­play rhyth­mic lip-lick­ing move­ments when pre­sented with sug­ary wa­ter, and both rats and hu­man in­fants dis­play a gap­ing re­ac­tion and mouth-wipes when pre­sented with bit­ter wa­ter.3

More­over, these an­i­mal lik­ing ex­pres­sions change in ways analo­gous to changes in hu­man sub­jec­tive plea­sure. Food is more plea­surable to us when we are hun­gry, and sweet tastes elicit more lik­ing ex­pres­sions in rats when they are hun­gry than when they are full.4 Similarly, both rats and hu­mans re­spond to in­tense doses of salt (more con­cen­trated than in sea­wa­ter) with mouth gapes and other aver­sive re­ac­tions, and hu­mans re­port sub­jec­tive dis­plea­sure. But if hu­mans or rats are de­pleted of salt, both hu­mans and rats re­act in­stead with lik­ing ex­pres­sions (lip-lick­ing), and hu­mans re­port sub­jec­tive plea­sure.5

Luck­ily, these lik­ing and dis­lik­ing ex­pres­sions share a com­mon evolu­tion­ary his­tory, and use the same brain struc­tures in rats, pri­mates, and hu­mans. Thus, fMRI scans have un­cov­ered to some de­gree the neu­ral cor­re­lates of plea­sure, giv­ing us an­other ob­jec­tive mea­sure of plea­sure.6

As for want­ing, re­search has re­vealed that dopamine is nec­es­sary for want­ing but not for lik­ing, and that dopamine largely causes want­ing.7

Now we are ready to ex­plain how we know that we do not de­sire plea­sure alone.

First, one can ex­pe­rience plea­sure even if dopamine-gen­er­at­ing struc­tures have been de­stroyed or de­pleted.8 Cho­co­late milk still tastes just as plea­surable de­spite the se­vere re­duc­tion of dopamine neu­rons in pa­tients suffer­ing from Park­in­son’s dis­ease,9 and the plea­sure of am­phetamine and co­caine per­sists through­out the use of dopamine-block­ing drugs or dietary-in­duced dopamine de­ple­tion — even while these same treat­ments do sup­press the want­ing of am­phetamine and co­caine.10

Se­cond, ele­va­tion of dopamine causes an in­crease in want­ing, but does not cause an in­crease in lik­ing (when the goal is ob­tained). For ex­am­ple, mice with raised dopamine lev­els work harder and re­sist dis­trac­tions more (com­pared to mice with nor­mal dopamine lev­els) to ob­tain sweet food re­wards, but they don’t ex­hibit stronger lik­ing re­ac­tions when they ob­tain the re­wards.11 In hu­mans, drug-in­duced dopamine in­creases cor­re­late well with sub­jec­tive rat­ings of ‘want­ing’ to take more of the drug, but not with rat­ings of ‘lik­ing’ that drug.12 In these cases, it be­comes clear that we want some things be­sides the plea­sure that usu­ally re­sults when we get what we want.

In­deed, it ap­pears that mam­mals can come to want some­thing that they have never be­fore ex­pe­rienced plea­sure when get­ting. In one study,13 re­searchers ob­served the neu­ral cor­re­lates of want­ing while feed­ing rats in­tense doses of salt dur­ing their very first time in a state of salt-de­ple­tion. That is, the rats had never be­fore ex­pe­rienced in­tense doses of salt as plea­surable (be­cause they had never been salt-de­pleted be­fore), and yet they wanted salt the very first time they en­coun­tered it in a salt-de­pleted state.

Com­min­gled signals

But why are lik­ing and want­ing so com­min­gled that we might con­fuse the two, or think that the only thing we de­sire is plea­sure? It may be be­cause the two differ­ent sig­nals are liter­ally com­min­gled on the same neu­rons. Re­sarchers ex­plain:

Mul­ti­plexed sig­nals com­min­gle in a man­ner akin to how wire and op­ti­cal com­mu­ni­ca­tion sys­tems carry tele­phone or com­puter data sig­nals from mul­ti­ple tele­phone con­ver­sa­tions, email com­mu­ni­ca­tions, and in­ter­net web traf­fic over a sin­gle wire. Just as the differ­ent sig­nals can be re­solved at their des­ti­na­tion by re­ceivers that de­code ap­pro­pri­ately, we be­lieve that mul­ti­ple re­ward sig­nals [lik­ing, want­ing, and learn­ing] can be packed into the ac­tivity of sin­gle ven­tral pal­li­dal neu­rons in much the same way, for po­ten­tial un­pack­ing down­stream.

......we have ob­served a sin­gle neu­ron to en­code all three sig­nals… at var­i­ous mo­ments or in differ­ent ways (Smith et al., 2007; Tin­dell et al., 2005).14


In the last decade, neu­ro­science has con­firmed what in­tu­ition could only sug­gest: that we de­sire more than plea­sure. We act not for the sake of plea­sure alone. We can­not solve the Friendly AI prob­lem just by pro­gram­ming an AI to max­i­mize plea­sure.


1 Noz­ick (1974), pp. 44-45.

2 Steiner (1973); Steiner et al (2001).

3 Grill & Ber­ridge (1985); Grill & Nor­gren (1978).

4 Ber­ridge (2000).

5 Ber­ridge et al. (1984); Schulkin (1991); Tin­dell et al. (2006).

6 Ber­ridge (2009).

7 Ber­ridge (2007); Robin­son & Ber­ridge (2003).

8 Ber­ridge & Robin­son (1998); Ber­ridge et al. (1989); Pecina et al. (1997).

9 Sienkiewicz-Jarosz et al. (2005).

10 Brauer et al. (2001); Brauer & de Wit (1997); Ley­ton (2009); Ley­ton et al. (2005).

11 Cag­niard et al. (2006); Pecina et al. (2003); Tin­dell et al. (2005); Wyvell & Ber­ridge (2000).

12 Evans et al. (2006); Ley­ton et al. (2002).

13 Tin­dell et al. (2009).

13 Al­dridge & Ber­ridge (2009). See Smith et al. (2011) for more re­cent de­tails on com­min­gling.


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