by Joseph E. Bogen

Beginning with the well-informed review by Puccetti (Puccetti ,1973) there has been considerable discussion in this Journal on complete cerebral commissurotomy (CCC) and its importance for believing in a duality of brains, minds and/or persons. My interest in the philosophical implications exceeds my philosophical expertise. But I have had a considerable experience with the patients under discussion, so I write mainly to point out a few neurologic misconceptions, as they appear in the paper of D. N. Robinson (Robinson ,1976). One cannot philosophise constructively without first being clear about the facts.

Robinson (at the bottom of P 74) refers to ". . . the paradoxical ability of a patient to recognise familiar objects held in the hand but not to recognise the same object when presented for visual inspection . . .". This is the classical description of a so-called 'visual agnosia' but does not at all describe a CCC patient. The patient with CCC invariably names familiar objects when presented for visual inspection, or describes them accurately in the event that the objects' names are not known; this is in contrast to neither naming nor describing an object when held in the left hand (of the right-handed patient). A CCC patient may occasionally guess the nature (and hence the name) of an object in the left. hand when helped by certain minimal clues such as temperature, or a nociceptive (pain-causing) property of an object. Such clever guessing is often wrong, and when it is wrong the patient nevertheless with the same (left) hand correctly retrieves the misnamed article from an unseen collection. This sort of dissociation between conversational report and left hand behaviour has made a great impression on everyone who has actually seen it (and there are many).

I am not an expert on certain matters discussed by Robinson, such as backward masking. But the view expressed by Robinson (in the absence, apparently, of any personal experience with the patients under consideration) that the CCC syndrome is more like than it is unlike various psychiatric and neurologic disturbances of which he lists a goodly number, is quite at variance with my own experience as a clinician for twenty years, and is also at variance with the impressions of the many other neurologists, neurosurgeons and psychologists who have seen these patients at first hand (Bogen and Vogel ,1975).

Robinson refers (on P. 77) to "the blind-folded patient's ability to point" with the left hand to an object (just previously held in that hand) in spite of the fact that it cannot be named. It's important to understand that correct pointing (as distinguished from tactual selection) can only occur when the patient is able to see the collection of objects, of which one is to be pointed out. In other words, the blindfold must be removed after the test object has been removed from the patient's hand. After restoration of vision, when asked to point the patient will usually point to the correct object with the left hand. And then

having pointed (but not before) the patient can name the object or, if requested, point to it with the right hand.

This sort of lateralised dissociation does not depend upon the presence or absence of language. For example, the right hand (or manus, if you prefer) of a split-brain monkey cannot retrieve an object just recently presented to the left manus (and vice versa). The rat which is trained with information restricted to one hemisphere (by cortical spreading depression) cannot do the just learned problem with the untrained hemisphere. When discussing these, and a host of other data, workers in the field spontaneously talk about what a hemisphere is doing or has done.

If Robinson would like to know what one hemisphere can do (which is a great deal indeed), he might benefit from my recent review (Bogen ,1974). And he should certainlv avail himself of an opportunity to see humans who have only one hemisphere, of whom there are a good many (Smith [1974). Such individuals provide an appropriate opportunity for anyone who desires to show the inapplicability of the two-brain view for any particular phenomenon of 'mental duality' (such as backward masking), because the demonstration of such a 'duality' in hernispherectomised persons would be clear-cut evidence of the irrelevancy, for that phenomenon, of having two hemispheres. Those of us who have had considerable experience with both commissurotomised and hemispherectomised individuals can assure Robinson that the more striking features of the CCC syndrome do not and have never appeared in a hemispherectomised individual. The two-brain view is required to explain the CCC syndrome, even if such a view is not necessary for or even relevant to other examples of simultaneous awareness and unawareness. In fact, having come to the two-brain view because of the CCC syndrome, many of us are inclined to suspect that various other phenomena of 'mental duality' might have this particular physiologic basis. In our view, each supposed case of mental duality must be tested individually to see if it has its basis in (requires) the duality of the cerebral hemispheres.

Robinson implies (P. 77, third paragraph) that no reasonable person (he says, 'we') would attribute to a hemisphere such properties as a percept, memory or a judgment. He thereby excludes (from the set of reasonable persons) almost all of those investigators who have had direct contact with the data.

The simplest, most straightforward way to talk about the facts is to speak of what a hemisphere can or cannot do, might do, or has just done. So far as the svndrome following CCC is concerned, it is a plain (and surely relevant) fact that evervone who has worked with these patients (or the related animal experiments) for any length of time has eventually adopted this usage no matter what his or her original resistance may have been. This usage seems to be independent of the species studied as well as of the ideologic, philosophic or stylistic predilection of those who have had the relevant experiences. Among Communist scientists, attribution of mental states is usually eschewed with respect to any experimental subject; but they do speak of the capacities of individual hemispheres, as when they refer to ". . . the activating influence of one brain-half on the other . . .' (Mosidze et al. [1971, P. 768).

Consider next another group of Communist scientists, famous for their studies in the laboratory rat (Bures et al. ,1974):

Another investigator, who has had experience with rats, cats, monkeys and chimpanzees, dating from the very inception in the early 1950S of the split-brain experiments, has expounded -

Doty, a recent past president of the Societyfor Neuroscience summarised his views by saying,

And we note the following phraseology in a discussion of some striking split-brain experiments in monkeys:

And the foregoing typical observation is subject to the fact that

In the same vein are the opinions of eminent Hollanders, discussing their, experiments in monkeys:

An Italian scientist, fortified by a long experience with cats, has also done notable experiments with Intact (unoperated) humans from which he concluded,

to the influence of a famous professor on his young students, consider the words

of a mature, 1ndependently renowned scientist trained in a British tradition of

understatement:

Such manner of speech also appears In the same article with reference to the results of lateralised 1esions:

From another Commonwealth scientist we have:

A recent splendid review by Sperry includes the following paragraph:

SUMMARY

In his opening paragraph Robinson avers, "These patients can identify palpably

but not visually those otherwise familiar objects presented to the left hand.'" But they do identify the objects visually ! What he should have written is, 'These patients can identify manually (by correct retrieval or appropriate manipulation) but not verbally, those otherwise familiar objects presented to the left hand.' His misunderstanding of these and related facts likely contributes to his rejection of the following conclusions: