and negate materialism and to reinstate the spiritual self as the controller of the brain" (Eccles,
1994a, p. X). It's important to recognize that he understood his account "as a hypothesis in
Popperian scientific method" (Eccles, 1994a, p. IX; cf. Popper and Eccles, 1977, p. 375), and even
saw "empirical evidence" for dualism (Eccles, 1987, p. 295 ff.); therefore Eccles has to allow (and
reckon with) the possibility of an empirical refutation (Vaas, 1997b).
For Eccles, only minute fractions of the material world are associated with mental states
(subjective experiences): the liaison-brains. That is where the conscious mind grasps the neuronal
activities like a searchlight, selects and modulates what it is interested in and integrates it to a
unified experience. Eccles believes that there are special modules which are linked to the mind like
radio transmitters and receivers (Popper and Eccles, 1997, ch. E7). These modules consist of
what he called dendrons. A dendron is a composite made of the bunching of the apical dendrites of
pyramidal cells found especially in neocortical lamina V. According to Eccles (1994a, p. 136), "each
dendron is linked with a psychon, giving its own characteristic unitary experience". There are "forty
million psychons for an estimated forty million dendrons of the human brain" (p. 88 and 98). So all
mental events and experiences "are a composite of elemental or unitary mental events"; "each of
these psychons is reciprocally linked in some unique manner to its dendron" (p. 87).
In 1992, Eccles (1994a, ch. 9) tried to explain the mechanism of mind-brain interaction - for him:
the interplay between psychons and dendrons - on the basis of quantum effects. The mind
becomes neurally effective by momentarily increasing the probabilities for exocytosis in a whole
dendron without violating physical laws of conservation. The essential place of this interaction "is at
individual microsites, the presynaptic vesicular grids of the boutons" (p. 82). Mental influences "do
no more than alter the probability of emission of a vesicle already in apposition" (p. 73); they change
synaptic activities on the quantum mechanical level without violating the conservation of energy or
momentum and are able to increase (the probability of) exocytosis by quantum tunneling. This
holds not only for intentional acts, voluntary commands for instance, but also for attentional acts:
Attention can "activate any selected parts of the neocortex at will" and can increase the frequency of
the impulse discharges in the pyramidal cells of a dendron (p. 174); this dendron triggers the
excitation of its associated psychon to give an increased experience of a sensation, e.g., pain;
"conversely, if attention is concentrated elsewhere, there will be less activation of the dendrons of
the nociceptive cortex and pain will be alleviated" (Eccles, 1994b, p. 17). "[C]onsciousness is
experienced in the brain where you evoke it by your attention, which plays on selected areas of the
cerebral cortex to give excitation. That excitation leads to amplified dendron responses to sensory
inputs and so to psychon activations and consciousness. Superimposed on this simple attentional
operation there would be a continuing dialogue between attention by the self and the selected
neocortical areas with their sensory inputs" (Eccles, 1994a, p. 176).
Apart from philosophical problems of ontological interactionism in general and Eccles' dualism in
particular, this proposal runs into empirical difficulties, too. Here are ten arguments based on
empirical research against Eccles' empirical claims and ontological inferences.
(1) In earlier works, Eccles localized the "liaison-brain", where the Self should get into contact with
matter, mainly in the dominant cortex hemisphere (endowed with language) (Popper and Eccles,
1977, p. 326).
• However, there are examples (like that of nine year old Alex, born with Sturge-Weber syndrome)
of first language acquisition and remaining conscious after a complete ablation of the left
hemisphere (Vargha-Khadem et al., 1997).
• Furthermore, PET studies of right-handed healthy people demonstrate clearly that autobiographic
memories (thus, very intimate parts of Ecclesian Selves) are located in the nondominant
hemisphere (increase of activities in the right temporal cortex, (para)hippocampus, posterior
cingulate, insula, prefrontal cortex, decrease of various parts of the left cortex) (Fink et al., 1996).
• Eccles (e.g., 1987, 1994c) has speculated about the supplementary motor area (SMA) as the
physical stage for interaction with the mind's voluntary commands - i.e., as the working place for
free will. However, after temporary interruption of voluntary movements, there is an extensive
recovery even after a complete ablation of SMA (Kolb and Whishaw, 1996, p. 262).
If on the other hand attention can "activate any selected part of the neocortex at will", as Eccles
wrote more recently (1994a, p. 174, cf. p. 79), it is unclear why there are actually neuronal
constraints of consciousness and volition and why the Self cannot sail around specific impairments
of them.
(2) If the mind is in some ontological sense autonomous and independent of matter as
interactionism assumes, it is difficult to see why specific brain lesions affect imagination as well as