90 CHAPTER THREE
electric current to stimulate activity in a specific area of the brain, on the
left premotor cortex of fifty- two volunteers. Inducing brain activity in the
left premotor cortex affects nerves in the right half of the body. By plac-
ing electrodes on the wrists and palms, Fecteau et al. calculated the neural
responses (motor evoked potentials, or meps) to the pulses administered
in the subjects’ right hands. The broad aim of the experiment was to ex-
plore whether they could modulate the effects of the pulses (as measured
by meps) by exposing research subjects to visual stimuli, and to discover
the conditions under which different stimuli could affect those responses.
In other words, could they modulate neural firing by adding meaningful
context?
In the first experiment Fecteau et al. showed the subjects pictures of
right and left hands, asking them to count fingers, and pictures of five dots
that were placed in positions that sparsely mimicked the tips of fingers in
right- and left- hand positions. In between they administered tms pulses
and measured the amplitude of the mep in the subjects’ own hands. They
reported that the effect of the visual stimuli on the excitability of the motor
cortex differed between the hands and the dots. When subjects were shown
pictures of hands, researchers recorded a difference between seeing pictures
of the right hand and the left. (More activation was recorded in the right
wrist when seeing pictures of the right hand than pictures of the left hand.)
The pictures of dots had no such effect between left and right. In the second
experiment they wanted to see whether prior exposure to the hand stimuli
could make a difference in how the dots modulated the firing of the premo-
tor cortex. In other words, could they manipulate the conditions so that the
premotor cortex would respond to the dots in the same way it responded to
the hands? They showed one group of subjects two blocks of hands, then a
block of dots, and compared this with a group who saw only dots. The first
group of subjects (those who saw the hands first) showed greater excitabil-
ity to the dots (between right and left orientation) than those who did not.
Fecteau et al. believe this means that a dot can be neurally received as a
representation of a hand in the context of prior information: “a dot in itself
does not elicit a specific response but can become meaningful depending
on what the subjects believe the dot motion represents” (175). A dot can be
a hand, in other words, if I recall the hand when seeing the dot and make
an inference. Fecteau et al. argue for “significant malleability in the way that