Consciousness

can produce ‘anarchic hand’ syndrome
in which the patient’s two hands fight
to produce opposite effects – for exam-
ple, one trying to undo a button while
the other tries to do it up.

Single-cell recording in monkeys has
explored the neuronal mechanisms of
voluntary control of behaviour (Schultz,
1999), and newer methods of brain
imaging have studied the functional
anatomy of volition in humans. In an
early study using PET, Chris Frith and
colleagues (1991) compared condi-
tions in which participants had either
to repeat a given word or choose one.
Subtracting the activity in one condi-
tion from the other revealed a differ-
ence in the left dorsolateral prefrontal
cortex (DLPFC) and anterior cingulate. Other similar studies showed increased
activity in DLPFC when actions were being selected and initiated. Reviewing
such studies, Spence and Frith (1999) conclude that even the simplest motor
procedures require complex and distributed neuronal activity, but the DLPFC
seems to be uniquely associated with the subjective experience of deciding
when and how to act.

Imagine you have to choose between your favourite brand of coffee or another
slightly cheaper one, or between buying that expensive plane ticket now in case
the flight sells out, or waiting in case it gets cheaper. Or perhaps, in an exper-
iment, you can take 45 pence now or have a 50:50 chance of getting either a
pound or nothing. What do you do? What does your brain do? These are the kinds
of situations found in neuroeconomics, the study of the brain bases of economic
behaviour (Politser, 2008; Rangel, Camerer, and Montague, 2008; Glimcher and
Fehr, 2013).

Even unconscious motivations can be measured. In one experiment, participants
saw either a pound coin or a penny coin, and the force they exerted by gripping a
handle determined how much they would get. They pressed harder for a share of
the pound even when it was presented subliminally and they could not say which
it was. Neuroimaging showed effects in part of the basal forebrain (Pessiglione et
al., 2007). This suggests the perhaps slightly worrying idea that unnoticed stimuli
around you are constantly affecting your motivations.

Now imagine that you are on a diet and tempted to succumb to a slice of choco-
late cake. When your hand stops just in time, who or what stopped it? Decisions
like this require what we think of as self-control to choose the option that is better
in the long run over one which is immediately tempting. In one study of dieters
making decisions about what to eat, fMRI scans suggested that the ventromedial
prefrontal cortex was involved in encoding goal values, while activity in the DLPFC
modulated these value signals when the participants were exercising self-control
(Hare, Camerer, and Rangel, 2009).

Early ‘whether

decision’

Motivations,

reasons for action

‘When decision’

Task selection

Action selection

Final predictive check

(forward model)

Action execution

External environment

‘What

decision’

Late ‘whether

decision’

FIGURE 9.2 • ‘A naturalized model of human

volition’ (Haggard, 2008,

Figure 2). Volition is modelled

as a set of decision processes

that each specify details of an

action. The decision whether to

perform an action (‘whether-

decision’) has both an early and

a motivational component and

a final predictive check. ‘What

decisions’ specify which goal or

task (from a range of tasks) to

perform (‘task selection’) and

the means by which to perform it

(‘action selection’). The timing of

voluntary actions often depends on

the combination of environmental

circumstances and internal

motivations: an explicit ‘when

decision’ is not always necessary

(Haggard, 2008).