Control Systems in the Living World - Building the Most Complex Structure on Earth - page 38

Under strictly experimental conditions, the behavior of an amoeba (formation
of pseudopodia, direction of its movements, beginning of reproductive activity, and
many physiological processes) is predictable. The amoeba's behavior is intended to
adapt it to the experimental challenges of the external environment. But intended
changes that bring about adaption imply that the system predicts * the adaptive result,
figures the ways and takes the steps to achieve it. But, if “prediction is computation”
( Pfaffmann and Zauner, 2001 ), where is the computation for determining the amoeba's
behavior made?
The father of modern neuroscience, the Spanish scientist Santiago Ramón y
Cajal, expressed the idea a century ago that the cytoskeleton is involved in conduct-
ing the nerve impulse and as early as 1951, the founding father of neurophysiology,
Charles Scott Sherrington, seemingly anticipated the present trend of looking at the
cytoskeleton as a potential “nervous system” of the cell in unicellulars:
Of nerve there is no trace. But the cell framework, the cyto-skeleton, might serve.
Sherrington (1951)
Indeed, neurons use the cytoskeleton to increase their potential computational
capacity at 10 16 bit states/s ( Rasmussen et al., 1990 ).
There is no experimentally verified mechanism of computation in microtubules of
the cytoskeleton. However, it is suggested that the cytoskeleton processes informa-
tion in unicellulars and in nerve cells. It is known, for example, that learning is asso-
ciated with increased production of tubulins (building blocks of microtubules) in the
brains of baby chicks and baby rats and higher activity of microtubules ( Hameroff,
1998; Tuszynski et al., 1998 ). It is thought that in neurons, microtubules may be uti-
lized in the processing of electrical information and in cognitive processing ( Priel
et al., 2006 ). There is adequate evidence to firmly assert that centrioles, the MTOCs
of the unicellulars, are organelles where such computation takes place. In this con-
text, it is important to remember that the proper placement of organelles within the
cell is also determined by the MTOC. Indeed, the improper positioning of centrioles
causes Chlamydomonas ' inability to move in the direction of the light source.
From the perspective of computational scientists, these unicellulars are bio-
logical micromachines, while the cytoskeleton appears to be their central system.
Responding to intrinsic and extrinsic signals, the cytoskeleton reorganizes to gen-
erate responses that adapt the cell to the changed external or internal environment
( Glade, 2008 ).
* While the conventional concept of prediction implies consciousness, today this term is homony-
mously used in biology and behavioral sciences to comprise unconscious adaptive behaviors of ani-
mals, including instinctive behaviors. This seems to be justiied because all of them have in common
input of the external stimulus, processing, and the output of the processing that manifests itself in the
predictable behavior. Instinctive behavior, like all predictable behaviors, implies computation regard-
less of whether it results from the activation of evolutionary stable circuits or from circuits that form in
response to speciic external stimuli.