Explaining Irrational Behavior

By Adam Leonard

Michael S. Gazzaniga is a pioneering neuroscientist in split-brain research who is currently Director of the SAGE Center for the Study of the Mind at the University of California, Santa Barbara. His books for non-scientists, from /The Social Brain/ (1985) to /The Ethical Brain/ (2006), have allowed anyone with an interest to follow the fascinating and revealing research being conducted with patients whose brain hemispheres had to be “split” (the connecting corpus callosum severed) to control life-threatening epilepsy.

The most intriguing – and potentially momentous – discovery arising from this research is not the much publicized left-brain, right-brain differences, but the uncovering of a function in the speaking hemisphere (usually the left-brain) that may prove instrumental to understanding Man’s recurring irrational behavior. The function, called the “interpreter,” apparently generates conscious and implicitly believed “rational” explanations for anything we do or feel in response to unconscious motivations.

Gazzaniga’s books describe how it is possible to provide information selectively to only the left (speaking) brain or the right (non-speaking) brain of a split-brain patient and monitor their responses. The startling discovery was that whenever the non-speaking brain was given a command to perform some action and the patient obeyed it, the speaking brain (which knew nothing of the command) would generate an explanation to explain the action … and would believe the explanation truly /was/ the reason for the action.

For example: the non-speaking brain could be instructed, “walk,” and the patient would stand up and begin walking away; if asked why, he (his speaking brain) would reply that he was going to get a drink, or a coke, or whatever. /Never/ would the speaking brain be nonplused or seem surprised by whatever action the non-speaking brain initiated, but would calmly explain it away with varying degrees of logic. … If the explanation seemed implausible and the patient was questioned about it, he would become annoyed, even angry, for he clearly believed it to be the true reason he’d performed the action.

The existence of the interpreter function has been known for over twenty years, and has been incorporated into Psychology’s explanations of self-deception, self-serving biases, cognitive dissonance, and defense mechanisms of the ego. What scientists have not yet addressed, however, is the possibility that the interpreter function explains how Man can be a tribal territorial animal (with DNA 98% the same as chimpanzees!) but totally unaware of any animal instincts affecting his behavior. … Is it possible that our chronic irrational behavior may actually be driven by instincts, but the interpreter covers this up by generating rational explanations for our irrational behavior, and convincing us the explanations are true? … Is it possible that the reason Man has never been able to live in peace is simply that as tribal territorial animals we compulsively form tribes and war with one another? … Is it possible that is also why we compulsively take sides and argue issues – such as this one – angrily and irrationally, as if they were territory to be taken or defended?



  1. These confabulation data are cool. Is there evidence that it plays a significant role in normal human behavior? How hard is it to elicit in normal subjects?

    I am always hesitant to extend results in a clinical subpopulation to make more general claims about the (normal) human condition.

    For instance, perhaps normal subjects don’t have this tendency at all because the left-hemisphere areas are tightly coupled to right-hemisphere areas, which together serve some purpose (e.g., rational thought as the right hemisphere provides data or constraints that work together with the storyteller to tell accurate stories, but when they are untethered, the confabulator runs on without friction from its usual contralateral partner, so it just spews out bull).

    So one relevant question, is there data about what area(s) on the left hemisphere are responsible for this confabulation, and what regions on the right side of the brain does it connect with?

  2. There is clear hemispheric asymmetries in terms of cognitive functional specializations (memory encoding visual discrimination, auditory processing…), and when examined with patient population (split brain patients) are more clear and evident as if there were two minds in a single physical brain.

    The right hemisphere have been associated with more visual and perceptual processes and the left with more logical or linguistic processes, the right processing negative emotions and the left more positive emotions…

    When a split brain patient is presented stimuli in the right visual hemisphere he can describe it verbally. And in the reverse order when confornted with visual stimuli in the left visual fixation area the patient remains mute, but he can use nonverbal cues to describe it (pointing etc.)

    In this sense there is a confabulation (the interpreter function)within the left hemisphere that provide us with the rationalitation of bechaviour because mayor cortical connections are disconnected but subcortical connections remain intact.

    How far this finding can be extent to explain other kinds of complex human behaviours, i don´t know.
    In response to the relevant question posed by Eric about what areas in
    the left hemisphere are responsible for the confabulation my guess is obviously broca´s area and its junction with other speech regions in the temporal and parietal lobes.

  3. Eric, it’s unlikely having normal access to the right-hemisphere ameliorates the phenomenon, since the right brain has no more knowledge to explain instinctive actions than does the left. As for whether “it plays a significant role in normal human behavior,” doesn’t the existence of “cool confabulation data” suggest that it does?

  4. Eric Thomson

    Well, this interesting data is in clinical subjects whose hemispheres have been severed from one another. My whole point is that we need to be careful of drawing inferences to normal subjects for all the reasons I mentioned and because of reasonable alternate hypotheses that need to be addressed.

  5. Eric Thomson

    One reason I am skeptical of how generally interesting this is is that even in clinical patients, they typically orient their eyes, body, and head to get a good integrated (two-hemisphere) look at the same thing. It is nontrivial to even create these stimuli etc … That is, it takes some work on the experimenter’s part to elicit these interesting phenomena. This suggests we aren’t normally just walking talking bullshitters all the time.

    That said, it  would be interesting to see under what conditions these patience confabulate, and under which conditions they don’t. Has science, for instance, combed its practices so that it is more like conditions in which people do not confabulate? I would also guess that philosophy is the opposite: institutionally sanctioned confabulation.

  6. Eric Thomson

    Crap, I just spelled ‘patients’ as ‘patience’. How embarassing.

    Wait, actually, no I meant to do that because I like to call split brain subjects ‘patience’ because they are so gentle and kind, their spirits are so patient and sweet. So I meant to do it.

    So that is one type of scenario in which I might be tempted to confabulate

  7. I don´t know if scientists when they are doing science and launching their hypothesis based on evidence and then forming theories are deactivating their interpreter centers

    and on the contrary, i don´t know if philosophers are not confabulating and then commanding and guiding their behaviour by more instinctual habits.

    As this thread is becoming more and more interesting due to the insightful, witty and double sword comments (with an ironic touch) made by Eric, perhaps i dare to email Gazzaniga himself, to join us.

  8. Brendan

    One does not need to appeal to split brain cases to find evidence for this sort of self-interpretation.

    Carruthers (forthcoming) “Introspection: Divided and Partially Eliminated” in PPR uses this sort of data to argue that much of what we take be introspectible is actually unconscious, and what we in fact instrospect is the product of self interpretation (roughly speaking).


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