|Antonio R. Damasio
EMOTION, REASON, AND THE HUMAN BRAIN
Grosset / Putnam 1994
|The investigation of patients with newly acquired
impairments of reasoning and decision making led to the identification
of a specific set of brain systems that were consistently damaged in those
patients. It also identified an apparently odd collection of neuropsychological
processes that depended on the integrity of those systems. What connects
those processes among themselves in the first place, and what links them
to the neural systems outlined in the previous chapter? The following paragraphs
offer some provisional answers.
1 First, reaching a decision about the typical personal problem posed in a social environment, which is complex and whose outcome is uncertain, requires both broad-based knowledge and reasoning strategies to operate over such knowledge. The broad knowledge includes facts about objects, persons, and situations in the external world. But because personal and social decisions are inextricable from survival, the knowledge also includes facts and mechanisms concerning the regulation of the organism as a whole. The reasoning strategies revolve around goals, options for action, predictions of future outcome, and plans for implementation of goals at varied time scales.
2 Second, the processes of emotion and feeling are part and parcel of the neural machinery for biological regulation, whose core is constituted by homeostatic controls, drives, and instincts.
3 Third, because of the brain's design, the requisite broad-based knowledge depends on numerous systems located in relatively separate brain regions rather than in one region. A large part of such knowledge is recalled in the form of images at many brain sites rather than at a single site. Although we have the illusion that everything comes together in a single anatomical theater, recent evidence suggests that it does not. Probably the relative simultaneity of activity at different sites binds the separate parts of the mind together.
4 Fourth, since knowledge can be retrieved only in distributed, parcellated manner, from sites in many parallel systems, the operation of reasoning strategies requires that the representation of myriad facts be held active in a broad parallel display for an extended period of time (in the very least for several seconds). In other words, the images over which we reason (images of specific objects, actions, and relational schemas; of words which help translate the latter into language form) not only must be "in focus"—something achieved by attention—but also must be "held active in mind"— something achieved by high-order working memory. I suspect that the mysterious alliance of the processes is due in part to the nature of the problem the organism is attempting to solve, and in part to the brain's design.
Personal and social decisions are fraught with uncertainty and have an impact on survival, directly or indirectly. Thus they require a vast repertoire of knowledge concerning the external world and the world within the organism. However, since the brain holds and retrieves knowledge in spatially segregated rather than integrated manner, they also require attention and working memory so that the component of knowledge that is retrieved as a display of images can be manipulated in time.
As for why the neural systems we identified overlap
so blatantly, I suspect evolutionary convenience is the answer. If basic
biological regulation is essential to the guidance of personal and social
behavior, then a brain design likely to have prevailed in natural selection
may have been one in which the subsystems responsible for reasoning and
decision making would have remained intimately interlocked with those concerned
with biological regulation, given their shared involvement in the business
The brain and the body are indissociably integrated
by mutually targeted biochemical and neural circuits. There are two principal
routes of interconnection. The route usually thought of first is made of
sensory and motor peripheral nerves which carry signals from every part
of the body to the brain, and from the brain to
Even a simplified summary reveals the intricacy of the relationships:
1 Nearly every part of the body, every muscle,
joint, and internal organ, can send signals to the brain via the peripheral
nerves. Those signals enter the brain at the level of the spinal cord or
the brain stem, and eventually are carried inside the brain, from neural
station to neural station, to the somatosensory cortices in the parietal
lobe and insular regions.
3 In the opposite direction, the brain can act,
through nerves, on all parts of the body. The agents for those actions
are the autonomic (or visceral) nervous system and the musculoskeletal
(or voluntary) nervous system. The signals for the autonomic nervous system
arise in the evolutionarily older regions (the amygdala, the cingulate,
the hypothalamus, and the brain stem), while the signals for the musculoskeletal
system arise in several motor cortices and subcortical motor nuclei, of
different evolutionary ages.
When I say that body and brain form an indissociable organism, I am not exaggerating. In fact, I am oversimplifying. Consider that the brain receives signals not only from the body but, in some of its sectors, from parts of itself that receive signals from the body! The organism constituted by the brain-body partnership interacts with the environment as an ensemble, the interaction being of neither the body nor the brain alone. But complex organisms such as ours do more than just interact, more than merely generate the spontaneous or reactive external responses known collectively as behavior. They also generate internal responses, some of which constitute images (visual, auditory, somatosensory, and so on), which I postulate as the basis for mind.
OF BEHAVIOR AND MIND
Many simple organisms, even those with only a single cell and no brain, perform actions spontaneously or in response to stimuli in the environment; that is, they produce behavior.
Some of these actions are contained in the organisms themselves, and can be either hidden to observers (for instance, a contraction in an interior organ), or externally observable (a tvvitch, or the extension of a limb). Other actions (crawling, walking, holding an object) are directed at the environment. But in some simple organisms and in all complex organisms, actions, whether spontaneous or reactive, are caused by commands from a brain. (Organisms with a body and no brain, but capable of movement, it should be noted, preceded and then coexisted with organisms that have both body and brain.) Not all actions commanded by a brain are caused by deliberation. On the contrary, it is a fair assumption that most so-called brain caused actions being taken at this very moment in the world are not deliberated at all. They are simple responses of which a reflex is an example: a stimulus conveyed by one neuron leading another neuron to act. As organisms acquired greater complexity, "brain-caused" actions required more intermediate processing. Other neurons were interpolated between the stimulus neuron and the response neuron, and varied parallel circuits were thus set up, but it did not follow that the organism with that more complicated brain necessarily had a mind. Brains can have many intervening steps in the circuits mediating between stimulus and response, and still have no mind, if they do not meet an essential condition: the ability to display images internally and to order those images in a process called thought. (The images are not solely visual; there are also "sound images," "olfactory images," and so on.) My statement about behaving organisms can now be completed by saying that not all have minds, that is, not all have mental phenomena (which is the same as saying that not all have cognition or cognitive processes). Some organisms have both behavior and cognition. Some have intelligent actions but no mind. No organism seems to have mind but no action.
My view then is that having a mind means that an organism forms neural representations which can become images, be manipulated in a process called thought, and eventually influence behavior by helping predict the future, plan accordingly, and choose the next action.
Herein lies the center of neurobiology as I see it: the process whereby neural representations, which consist of biological modifications created by learning in a neuron circuit, become images in our minds; the process that allows for invisible microstructural changes in neuron circuits (in cell bodies, dendrites and axons, and synapses) to become a neural representation, which in turn becomes an image we each experience as belonging to us.
To a first approximation, the overall function of the brain is to be well informed about what goes on in the rest of the body, the body proper; about what goes on in itself; and about the environment surrounding the organism, so that suitable, survivable accommodations can be achieved between organism and environment. From an evolutionary perspective, it is not the other way around. If there had been no body, there would have been no brain. Incidentally, the simple organisms with just body and behavior but no brain or mind are still here, and are in fact far more numerous than humans by several orders of magnitude. Think of the many happy bacteria such as Escherichia coli now living inside each of us.
ORGANISM AND ENVIRONMENT INTERACT:
If body and brain interact with each other intensely, the organism they form interacts with its surroundings no less so. Their relations are mediated by the organism's movement and its sensory devices.
The environment makes its mark on the organism in a variety of ways. One is by stimulating neural activity in the eye (inside which is in some symptoms of schizophrenia and other diseases. The fundamental problem created by time binding has to do with the requirement for maintaining focused activity at different sites for as long as necessary for meaningful combinations to be made and for reasoning and decision making to take place. In other words, time binding requires powerful and effective mechanisms of attention and working memory, and nature seems to have agreed to provide them.
Each sensory system appears equipped to provide
its own local attention and working-memory devices. But when it comes to
the processes of global attention and working memory, human studies as
well as animal experiments suggest that the prefrontal cortices and some
limbic system structures (the anterior cingulate) are essential. The mysterious
connection between the processes and brain systems discussed at the beginning
of this chapter may be clearer now.
IMAGES OF NOW, IMAGES OF THE PAST
The factual knowledge required for reasoning and decision making comes to the mind in the form of images. Let us look, however briefly, at the possible neural substrate of those images.
If you look out the window at the autumn landscape, or listen to the music playing in the background, or run your fingers over a smooth metal surface, or read these words, line after line down this page, you are perceiving, and thereby forming images of varied sensory modalities. The images so formed are called perceptual images.
But you may stop attending to that landscape or music or surface or text, distract yourself from it, and turn your thoughts elsewhere. Perhaps you are now thinking of your Aunt Maggie, or the Eiffel Tower, or the voice of Placido Domingo, or of what I just said about images. Any of those thoughts is also constituted by images, regardless of whether they are made~up mostly of shapes, colors, movements, tones, or spoken or unspoken words. Those images, which occur as you conjure up a remembrance of things past, are known as recalled images, so as to distinguish them from the perceptual variety.
By using recalled images you can bring back a particular type of past image, one formed when you planned something that has not yet happened but that you intend to have happen, for example, reorganizing your library come this weekend. As the planning process unfolded, you were forming images of objects and movements, and consolidating a memory of that fiction in your mind. Images of something that has not yet happened and that may in fact never come to pass are no different in nature from the images you hold of something that already has happened. They constitute the memory of a possible future rather than of the past that was. These various images—perceptual, recalled from real past, and recalled from plans of the future—are constructions of your organism's brain. All that you can know for certain is that they are real to your self, and that other beings make comparable images. We share our image-based concept of the world with other humans~ and even with some animals; there is a remarkable consistency in the constructions different individuals make of the essential aspects of the environment (textures, sounds, shapes, colors, space). If our organisms were designed differently, the constructions we make of the world around us would be different as well. We do not know, and it is improbable that we will ever know, what "absolute" reality is like.
How do we come to create these marvelous constructions? It appears they are concocted by a complex neural machinery of perception, memory, and reasoning. Sometimes the construction is paced from the world outside the brain, that is, from the world inside our body or around it, with a bit of help from past memory. That is the case when we generate perceptual images. Sometimes the construction is directed entirely from within our brain, by our sweet and silent thought process, from the top down, as it were.
That is the case, for instance, when we recall a favorite melody, or recall visual scenes with our eyes closed and covered, whether the scenes are a replaying of a real event or an imagined one.
But the neural activity that is most closely related to the images we experience occurs in early sensory cortices and not in the other regions. The activity in the early sensory cortices, whether it is engaged by perception or by recall of memories, is a result, so to speak, of complex processes operating behind the scenes, in numerous regions of the cerebral cortex and of neuron nuclei beneath the cortex, in basal ganglia, brain stem, and elsewhere. In short: Images are based directly on those neural representations, and only those which are organized topographically and which occur in early sensory cortices. But they are formed either under the control of sensory receptors oriented to the brain's outside (e.g., a retina), or under the control of dispositional representations (dispositions) contained inside the brain, in cortical regions and subcortical nuclei.
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