Aspects Of Mind
Contemporary cognitive neuroscience has made important strides in analyzing the mind. Three areas of particularly intense research are perception, emotion, and consciousness.
Contemporary cognitive neuroscience focuses on aspects of mind that are both important and scientifically tractable. A vast amount of research has been carried out on perception, and in particular, on vision. Researchers have repeatedly demonstrated that the mind does not simply perceive a photograph-like representation of the world. That would demand far more information than the brain can handle. Even if the mind could cope with such a torrent of data, it would probably miss the most important aspects of what is seen—for example, a carelessly driven car lurching onto the road.
Instead, the visual perception system searches for certain patterns. If one sees a few fragmentary lines aligned together, the lines are automatically perceived as a single edge. Different parts of the visual system are tuned to different patterns; some neurons are most sensitive to movement, for example, while others are sensitive to contrasts. These regions are arranged in a pathway, with the first regions along the pathway handling simple processing and then passing on information to regions that can recognize more abstract information, such as faces.
Among the investigations of the mind, emotions have posed a particularly difficult challenge. Medieval European thinkers ascribed many of the states called emotions to souls residing in the heart and liver, or to the four humors. Descartes helped to render these explanations obsolete, but his dualism posed problems of its own. Having divided the human being into two distinct substances—body and mind—he had to struggle to find an explanation for emotions. Emotions clearly affect the body, raising heart rate, causing one to blush, and so on. And yet humans also generally used their powers of reason to reach goals, which can be motivated by emotions. Fear of a fire, for example, might spur someone to figure out the fastest way out of a burning building. So somehow emotions must be able to influence the soul, despite the soul being made of a separate substance than the body.
Descartes envisioned passions as purely physical phenomena that could influence the mind by acting on the pineal gland, the soul's intersection with the body. The function of the passions, Descartes argued, was to dispose the soul to want the things that are useful, and to dispose the body to make the movements that would help to acquire those things. But he also argued that passions can cause suffering and thus need to be mastered by the soul. Descartes defined this mastery as wisdom.
Contemporary neuroscientists are weaning themselves from Descartes's dualism in their studies of emotions. They recognize human emotions as having a long evolutionary history. Emotions originated hundreds of millions of years ago as adaptive responses that simpler animals produced in response to a changing environment. Signs of danger, for example, triggered releases of hormones that prepared animals to fight or flee. Signs of potential reward (such as food or a mate) triggered release of neurotransmitters that caused feelings of anticipation and heightened attention.
While human emotions share a common ancestry with reactions in other animals, they are modified for the peculiarities of the human species. Fear is a case in point. Humans and other vertebrates rely on a region of the brain known as the amygdala to produce a sense of fear and vigilance. Rats learn to fear a flash of light if it reliably precedes an electric shock; remove their amygdala, and they never make the association. Humans with lesions in the amygdala also fail this test. But brain imaging shows that the human amygdala is also extremely sensitive to facial expressions. It takes only a few hundredths of a second for the amygdala to respond to an angry face, long before one becomes consciously aware of perceiving it. This is not surprising, given that humans are an intensely social species.
Emotions are also intimately involved in the most abstract thinking of which humans are capable. For example, Antonio Damasio (b. 1944) of the University of Iowa has shown that lesions to an emotion-associated region called the orbitofrontal cortex can lead to poor decision making. Damasio hypothesizes that normally people are guided by emotional reactions to memories of relevant experiences in the past.
While cognitive neuroscientists have made great strides in identifying the components of the mind, they have much left to learn about their integration. Perhaps the most powerful example of this challenge is consciousness. Neuroscientists long shied away from the question of consciousness, feeling that it was impossible to formulate a scientific program to study it. At the close of the twentieth century, though, they began to overcome their reticence and began making serious attempts to solve this mystery.
Consciousness refers to people's awareness of themselves and of their own experiences. At the same time, philosophers also see in consciousness a feature known as qualia: the subjective experience generated in each person's brain. To appreciate the difficulty of studying qualia, imagine a neuroscientist who lacks color vision, seeing the world only in black and white. Imagine that she succeeds in learning everything there is to know about how the retina transfers information about different frequencies of light to the brain, and how the brain processes that information. But she does not know what it is like to experience the sight of red, or any other color. These qualia remain beyond her reach.
Despite these conceptual obstacles, neuroscientists are beginning to study consciousness. Some are using fMRI to compare the human brain in different states of consciousness. For example, scientists can measure the differences in the brain before it is aware of seeing an object and afterwards. They can also compare unconscious processing of sensory information versus conscious processing. In another line of research, scientists place electrodes on a subject's scalp in order to take high-resolution recordings of brain waves, looking for changes in frequencies that might represent signatures of consciousness.
Such studies do not pinpoint a "consciousness organ" in the brain. Rather, they offer an increasingly detailed picture of neural activity that correlate with conscious experiences. In one model that has emerged from this work, brain waves produced in different parts of the brain become synchronized during consciousness, producing a "global workspace" in which the processes going on in different parts of the brain are united.
There are a number of other models that are being explored, however, and none has emerged as a clear favorite over the others. Some researchers have suggested that the study of consciousness in the twenty-first century is like the study of hurricanes in the 1800s. Nineteenth-century meteorologists could collect very little data in order to understand and predict hurricanes. They could take readings of air pressure, winds, and rainfall at a few weather stations, and then try to extrapolate those results. Only when weather satellites were launched into orbit were meteorologists able to see an entire hurricane and track it across the Atlantic. In order to produce a satisfying theory of consciousness, scientists may have to wait for the arrival of satellites for the mind.
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