Self And The Phenomenon Of Life: A Biologist Examines Life From Molecules To Humanity

Self and Free Will 249

“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanity

is fed back from muscle, tendon, and vision through sensory fibers to
an evaluative center in the parietal cortex, and eventually to the supple-
mentary motor, the premotor, and the prefrontal areas. The constant
sensory feedback provides a mechanism for fine-tuning the motion.
In addition, through a corollary discharge system, feed-forward sig-
nals are sent from the supplementary motor area, the premotor area,
and primary motor area to the parietal cortex evaluative center, where
comparison is constantly made with the feedback information. A correct
matching between feed-forward and feedback messages likely produces
a sense of agency, the subjective feeling of work accomplished (volition).
It is interesting to note that electrical stimulation of the inferior part
of the posterior parietal cortex alone induces the experience of inten-
tion to move as well as the experience of motion, even though no actual
muscle movement has occurred, thus implicating the participation of the
parietal cortex in the generation of “free will.”^17
I should hasten to add that, although the matching of forward and
backward messages in the parietal cortex satisfies the sense of agency
in terms of a single voluntary act (such as flexing the arm), it is far too

Fig. 11.4. Human brain (left cerebral hemisphere viewed from the outside, head
pointing left) showing areas of the cerebral cortex involved in volitional action. [Refer to
Fig. 11.3; also compare with Fig. 7.10 in Chapter 7.]