Le neuroscienze decretano la fine del libero arbitrio? Di Michele Forastiere (michele.forastiere@gmail.com),  13 gennaio, 2012, http://www.uccronline.it

Prenderò spunto da un recente articolo di Eddy Nahmias, intitolato “Is Neuroscience the Death of Free Will?” (“Le neuroscienze sono la morte per il libero arbitrio?”), per affrontare la questione del libero arbitrio – un’impresa, per la verità, in cui da tempo mi ero ripromesso di imbarcarmi. Nahmias, professore associato presso il Dipartimento di Filosofia e l’Istituto di Neuroscienze della Georgia State University, inizia col constatare la crescente diffusione dell’idea che le ricerche neuroscientifiche dimostrerebbero, in maniera ormai inequivocabile, l’illusorietà del libero arbitrio. C’è addirittura chi è sicuro che ogni comportamento dell’Uomo possa essere spiegato mediante il funzionamento meccanicistico di uno o più circuiti neuronali. Niente di nuovo sotto il sole: si ricorderà che questa posizione è sostenuta anche dal “nostro” Edoardo Boncinelli (cfr. Ultimissima 14/9/11).

Intanto è bene sottolineare che un’idea del genere – se fosse realmente confermata – non sarebbe priva di importanti conseguenze pratiche. In particolare, se il libero arbitrio fosse morto, allora anche la responsabilità morale e legale sarebbe moribonda. Lo sostiene l’analista legale del New York Times, Jeffrey Rosen, che dice: “Dal momento che il comportamento è causato dal nostro cervello, ciò non significherebbe che ogni azione potrebbe essere potenzialmente scusata?”. Torna alla mente la notizia, riportata qualche mese fa dal Corriere della Sera, del riconoscimento di una peculiare attenuante in un delitto: la presenza di “alterazioni in un’area del cervello che ha la funzione di regolare le azioni aggressive”. Come dire che l’azione criminale sarebbe stata determinata (almeno in parte) da un inesorabile meccanismo biochimico, e non direttamente dalla volontà dell’imputata. Detto in altri termini, se la capacità di discriminazione è solo l’effetto di una serie di scariche elettrochimiche nei neuroni… ebbene, nessuna azione, nessun pensiero, nessuna decisione si possono definire “liberi” e “volontari”: facciamo quel che facciamo perché non possiamo fare altrimenti.

A questo punto sarebbe necessario aprire un discorso più generale sul determinismo causale, secondo cui ogni cosa che accade è inevitabile, non importa ciò che pensiamo o proviamo a fare. Limitandoci per il momento alla sua applicazione al funzionamento della mente umana, è facile capire che esso costituisce la negazione del libero arbitrio: se le nostre decisioni non sono altro che reazioni chimiche, allora il nostro pensiero conscio viene costantemente scavalcato da ciò che il cervello meccanicamente fa – così che ogni nostra azione si può ritenere di fatto involontaria. Nahmias, però, pensa che, anche nel caso in cui le neuroscienze e la psicologia fossero in grado di stabilire la verità del determinismo – cosa che ritiene improbabile – ciò non implicherebbe che il pensiero conscio venga effettivamente scavalcato. Tutto sta nel definire correttamente l’esercizio del libero arbitrio come uso efficace delle capacità di decisione consapevole e di autocontrollo. È chiaro che questa è una definizione pragmatica, che non dice nulla sul presunto determinismo di fondo della realtà (su questo torneremo più avanti); però è in grado di stabilire un punto importante, e cioè che la responsabilità personale di ogni atto che implichi decisioni moralmente rilevanti non può essere in nessun caso annullata.

Vediamo brevemente su quali basi Nahmias poggia la sua convinzione. È vero – dice – che alcuni esperimenti sembrano suggerire che le capacità di decisione consapevole siano escluse dalle catene causali che producono le nostre decisioni e azioni; in particolare, è vero che le neuroscienze mostrano che il nostro cervello prende certe decisioni prima che ne siamo consapevoli. In effetti, però, gli esperimenti riguardano tutti decisioni rapide e ripetitive, per le quali era stato detto ai soggetti di non pianificare l’azione, ma di aspettare l’insorgere di un forte stimolo a compierla. L’attività neurale precoce misurata, dunque, corrispondeva molto semplicemente a stimoli elementari che precedevano la consapevolezza conscia. D’altra parte, questo è ciò che dobbiamo ragionevolmente aspettarci in corrispondenza di decisioni semplici e ripetitive! Se, infatti, fossimo costretti a riflettere consapevolmente su ogni nostra azione, saremmo degli inetti a vita: saremmo perenni principianti alla guida, incapaci di parlare, scrivere, ballare, suonare uno strumento. È chiaro che l’attenzione conscia, relativamente lenta e laboriosa, è richiesta quando si apprende una qualsiasi attività; dopo è sostituita da processi neurali inconsci, molto più rapidi, in cui la consapevolezza gioca esclusivamente un ruolo di controllo a posteriori. È altrettanto chiaro, però, che essa è indispensabile nelle questioni importanti, quando per esempio è necessario giudicare o pianificare. Ebbene – ribadisce Nahmias – le neuroscienze e la psicologia non forniscono alcuna prova del fatto che la consapevolezza cosciente non intervenga in quel genere di decisioni: anzi, esistono prove concrete che indicano esattamente il contrario.

Secondo Nahmias, dunque, le indagini neuroscientifiche dovrebbero partire dall’assunto che le attività di decisione consapevole e di pensiero razionale siano svolte da complicati processi cerebrali, dopodiché potrebbero procedere a valutare se quei processi abbiano o non abbiano un ruolo causale nell’azione. In realtà, egli ritiene assai improbabile che i futuri sviluppi delle neuroscienze riusciranno a dimostrare la seconda possibilità: vorrebbe dire che quei processi cerebrali non sono di nessuna utilità pratica – anzi, sono sostanzialmente dannosi, considerata la notevole quantità di energia necessaria al loro funzionamento. Detto in altri termini, in quel caso l’autocoscienza si rivelerebbe essere poco più di un inutile accessorio, evolutosi per puro caso con l’unica funzione di permetterci di osservare ciò che facciamo dopo il fatto, piuttosto che per affinare le nostre procedure decisionali e migliorare il comportamento. In conclusione, Nahmias osserva che non c’è dubbio che i nostri processi cerebrali consci siano troppo lenti per intervenire ogni volta che si flette un dito per battere al computer; ma fin tanto che essi fanno la loro parte nel decidere quali idee scrivere, possiamo affermare che non sono un’appendice superflua, e che il libero arbitrio non è scavalcato da ciò che il cervello fa.

A questo punto, direi che si possa tranquillamente rispondere alla domanda iniziale con un “no”: le neuroscienze non decretano la fine del libero arbitrio – quanto meno nell’accezione pragmatica qui proposta. Questo, però, non risolve il problema generale del determinismo causale cui accennavo prima. Insomma, se anche il complesso delle funzioni cerebrali che presiedono alla decisione consapevole dipende, in ultima analisi, da meccanismi elettrochimici neuronali, si può continuare a parlare di libero arbitrio in senso proprio? In altre parole, posso dire di decidere davvero liberamente, se la mia stessa autocoscienza non è altro che il risultato di una concatenazione di reazioni chimiche, la cui consequenzialità è tanto inevitabile quanto la caduta di un sasso lungo un pendio?

Credo proprio che questo argomento meriti una trattazione ampia e approfondita… che proveremo ad affrontare in un prossimo articolo.

L’articolo originale

November 13, 2011, 5:25 pm

Is Neuroscience the Death of Free Will?

By EDDY NAHMIAS

Is free will an illusion?  Some leading scientists think so.  For instance, in 2002 the psychologist Daniel Wegner wrote , “It seems we are agents. It seems we cause what we do… It is sobering and ultimately accurate to call all this an illusion.” More recently, the neuroscientist Patrick Haggard declared , “We certainly don’t have free will.  Not in the sense we think.”  And in June, the neuroscientist Sam Harris claimed , “You seem to be an agent acting of your own free will. The problem, however, is that this point of view cannot be reconciled with what we know about the human brain.”

Many neuroscientists are employing a flawed notion of free will.

Such proclamations make the news; after all, if free will is dead, then moral and legal responsibility may be close behind.  As the legal analyst Jeffrey Rosen wrote in The New York Times Magazine, “Since all behavior is caused by our brains, wouldn’t this mean all behavior could potentially be excused? … The death of free will, or its exposure as a convenient illusion, some worry, could wreak havoc on our sense of moral and legal responsibility.”

Indeed, free will matters in part because it is a precondition for deserving blame for bad acts and deserving credit for achievements.  It also turns out that simply exposing people to scientific claims that free will is an illusion can lead them to misbehave , for instance, cheating more or helping others less. [1]  So, it matters whether these scientists are justified in concluding that free will is an illusion.

Here, I’ll explain why neuroscience is not the death of free will and does not “wreak havoc on our sense of moral and legal responsibility,” extending a discussion begun in Gary Gutting’s recent Stone column .  I’ll argue that the neuroscientific evidence does not undermine free will.  But first, I’ll explain the central problem: these scientists are employing a flawed notion of free will.  Once a better notion of free will is in place, the argument can be turned on its head.  Instead of showing that free will is an illusion, neuroscience and psychology can actually help us understand how it works.

When Haggard concludes that we do not have free will “in the sense we think,” he reveals how this conclusion depends on a particular definition of free will.  Scientists’ arguments that free will is an illusion typically begin by assuming that free will, by definition, requires an immaterial soul or non-physical mind, and they take neuroscience to provide evidence that our minds are physical.  Haggard mentions free will “in the spiritual sense … a ghost in the machine.”  The neuroscientist Read Montague defines free will as “the idea that we make choices and have thoughts independent of anything remotely resembling a physical process. Free will is the close cousin to the idea of the soul” (Current Biology 18, 2008).[2] They use a definition of free will that they take to be demanded by ordinary thinking and philosophical theory.  But they are mistaken on both counts.

We should be wary of defining things out of existence.  Define Earth as the planet at the center of the universe and it turns out there is no Earth.  Define what’s moral as whatever your God mandates and suddenly most people become immoral.  Define marriage as a union only for procreation, and you thereby annul many marriages.

The sciences of the mind do give us good reasons to think that our minds are made of matter.  But to conclude that consciousness or free will is thereby an illusion is too quick.  It is like inferring from discoveries in organic chemistry that life is an illusion just because living organisms are made up of non-living stuff.  Much of the progress in science comes precisely from understanding wholes in terms of their parts, without this suggesting the disappearance of the wholes.  There’s no reason to define the mind or free will in a way that begins by cutting off this possibility for progress.

Our brains are the most complexly organized things in the known universe, just the sort of thing that could eventually make sense of why each of us is unique, why we are conscious creatures and why humans have abilities to comprehend, converse, and create that go well beyond the precursors of these abilities in other animals.  Neuroscientific discoveries over the next century will uncover how consciousness and thinking work the way they do because our complex brains work the way they do.

Our capacities for conscious deliberation, rational thinking and self-control are not magical abilities.

These discoveries about how our brains work can also explain how free will works rather than explaining it away.  But first, we need to define free will in a more reasonable and useful way.  Many philosophers, including me, understand free will as a set of capacities for imagining future courses of action, deliberating about one’s reasons for choosing them, planning one’s actions in light of this deliberation and controlling actions in the face of competing desires.  We act of our own free will to the extent that we have the opportunity to exercise these capacities, without unreasonable external or internal pressure.  We are responsible for our actions roughly to the extent that we possess these capacities and we have opportunities to exercise them.

These capacities for conscious deliberation, rational thinking and self-control are not magical abilities.  They need not belong to immaterial souls outside the realm of scientific understanding (indeed, since we don’t know how souls are supposed to work, souls would not help to explain these capacities).  Rather, these are the sorts of cognitive capacities that psychologists and neuroscientists are well positioned to study.

This conception of free will represents a longstanding and dominant view in philosophy, though it is typically ignored by scientists who conclude that free will is an illusion.  It also turns out that most non-philosophers have intuitions about free and responsible action that track this conception of free will.  Researchers in the new field of experimental philosophy study what “the folk” think about philosophical issues and why. For instance, my collaborators and I have found that most people think that free will and responsibility are compatible with determinism, the thesis that all events are part of a law-like chain of events such that earlier events necessitate later events.[3] That is, most people judge that you can have free will and be responsible for your actions even if all of your decisions and actions are entirely caused by earlier events in accord with natural laws.

Our studies suggest that people sometimes misunderstand determinism to mean that we are somehow cut out of this causal chain leading to our actions. People are threatened by a possibility I call “bypassing” — the idea that our actions are caused in ways that bypass our conscious deliberations and decisions.  So, if people mistakenly take causal determinism to mean that everything that happens is inevitable no matter what you think or try to do, then they conclude that we have no free will.  Or if determinism is presented in a way that suggests all our decisions are just chemical reactions, they take that to mean that our conscious thinking is bypassed in such a way that we lack free will.

Even if neuroscience and psychology were in a position to establish the truth of determinism — a job better left for physics — this would not establish bypassing.  As long as people understand that discoveries about how our brains work do not mean that what we think or try to do makes no difference to what happens, then their belief in free will is preserved.  What matters to people is that we have the capacities for conscious deliberation and self-control that I’ve suggested we identify with free will.

But what about neuroscientific evidence that seems to suggest that these capacities are cut out of the causal chains leading to our decisions and actions? For instance, doesn’t neuroscience show that our brains make decisions before we are conscious of them such that our conscious decisions are bypassed?  With these questions, we can move past the debates about whether free will requires souls or indeterminism — debates that neuroscience does not settle — and examine actual neuroscientific evidence.  Consider, for instance, research by neuroscientists suggesting that non-conscious processes in our brain cause our actions, while conscious awareness of what we are doing occurs later, too late to influence our behavior.  Some interpret this research as showing that consciousness is merely an observer of the output of non-conscious mechanisms.  Extending the paradigm developed by Benjamin Libet, John-Dylan Haynes and his collaborators used fMRI research to find patterns of neural activity in people’s brains that correlated with their decision to press either a right or left button up to seven seconds before they were aware of deciding which button to press.  Haynes concludes: “How can I call a will ‘mine’ if I don’t even know when it occurred and what it has decided to do?”

However, the existing evidence does not support the conclusion that free will is an illusion.  First of all, it does not show that a decision has been made before people are aware of having made it.  It simply finds discernible patterns of neural activity that precede decisions.  If we assume that conscious decisions have neural correlates, then we should expect to find early signs of those correlates “ramping up” to the moment of consciousness.  It would be miraculous if the brain did nothing at all until the moment when people became aware of a decision to move.  These experiments all involve quick, repetitive decisions, and people are told not to plan their decisions but just to wait for an urge to come upon them.  The early neural activity measured in the experiments likely represents these urges or other preparations for movement that precede conscious awareness.

This is what we should expect with simple decisions.  Indeed, we are lucky that conscious thinking plays little or no role in quick or habitual decisions and actions.  If we had to consciously consider our every move, we’d be bumbling fools.  We’d be like perpetual beginners at tennis, overthinking every stroke.  We’d be unable to speak fluently, much less dance or drive.  Often we initially attend consciously to what we are doing precisely to reach the point where we act without consciously attending to the component decisions and actions in our complex endeavors.  When we type, tango, or talk, we don’t want conscious thinking to precede every move we make, though we do want to be aware of what we’re doing and correct any mistakes we’re making.  Conscious attention is relatively slow and effortful.  We must use it wisely.

We need conscious deliberation to make a difference when it matters — when we have important decisions and plans to make.  The evidence from neuroscience and psychology has not shown that consciousness doesn’t matter in those sorts of decisions — in fact, some evidence suggests the opposite.  We should not begin by assuming that free will requires a conscious self that exists beyond the brain (where?), and then conclude that any evidence that shows brain processes precede action thereby demonstrates that consciousness is bypassed.  Rather, we should consider the role of consciousness in action on the assumption that our conscious deliberation and rational thinking are carried out by complex brain processes, and then we can examine whether those very brain processes play a causal role in action.

For example:  suppose I am trying to decide whether to give $1,000 to charity or buy a new TV.  I consciously consider the reasons for each choice — e.g., how it fits with my goals and values.  I gather information about each option.  Perhaps I struggle to overcome my more selfish motivations.  I decide based on this conscious reasoning (it certainly would not help if I could magically decide on no basis at all), and I act accordingly.  Now, let’s suppose each part of this process is carried out by processes in my brain.  If so, then to show that consciousness is bypassed would require evidence showing that thosevery brain processes underlying my conscious reasoning are dead-ends.  It would have to show that those brain processes do not connect up with the processes that lead to my typing my credit card number into the Best Buy Web site (I may then regret my selfish decision and re-evaluate my reasons for my future decisions).

None of the evidence marshaled by neuroscientists and psychologists suggests that those neural processes involved in the conscious aspects of such complex, temporally extended decision-making are in fact causal dead ends.  It would be almost unbelievable if such evidence turned up.  It would mean that whatever processes in the brain are involved in conscious deliberation and self-control — and the substantial energy these processes use — were as useless as our appendix, that they evolved only to observe what we do after the fact, rather than to improve our decision-making and behavior.  No doubt these conscious brain processes move too slowly to be involved in each finger flex as I type, but as long as they play their part in what I do down the road — such as considering what ideas to type up — then my conscious self is not a dead end, and it is a mistake to say my free will is bypassed by what my brain does.

So, does neuroscience mean the death of free will?  Well, it could if it somehow demonstrated that conscious deliberation and rational self-control did not really exist or that they worked in a sheltered corner of the brain that has no influence on our actions.  But neither of these possibilities is likely.  True, the mind sciences will continue to show that consciousness does not work in just the ways we thought, and they already suggest significant limitations on the extent of our rationality, self-knowledge, and self-control.  Such discoveries suggest that most of us possess less free will than we tend to think, and they may inform debates about our degrees of responsibility.  But they do not show that free will is an illusion.

If we put aside the misleading idea that free will depends on supernatural souls rather than our quite miraculous brains, and if we put aside the mistaken idea that our conscious thinking matters most in the milliseconds before movement, then neuroscience does not kill free will.  Rather, it can help to explain our capacities to control our actions in such a way that we are responsible for them. It can help us rediscover free will.