When examining the structure and function of the human brain it is necessary to account for the developed organ in the proper context. Edelman (2006) describes that an analysis of the brain must address the system “first during evolution and then during individual brain development” (p. 56). In studies of intelligence, it is often overlooked that the original purpose of the brain was to monitor all bodily functions including breathing, hunger, thirst, circadian rhythm and other basic life processes. Only a full understanding of the anatomy of the brain would allow for a comprehensive theory of higher brain functioning.
The brain, along with the spine, make up the central nervous system, the body’s communication and decision center. The spinal cord is a thick column of nerve tissue that extends from the base of the brain down the spine. The brain stem, which is the portion of the brain that is continuous with the spinal cord, controls bodily functions such as heartbeat, breathing and body temperature. At the upper end of the brain stem lies the diencephalon which regulates hunger pangs, sleeps cycles and circadian rhythms. This part of the central, inner brain before the limbic area is known as the reptilian brain. Three major structures in this area are the thalamus, hypothalamus and pineal gland. The hypothalamus is involved with aggression, fear, sexual behavior and helps regulate temperature, water, appetite and thirst. The thalamus is a central structure that organizes and sends messages to different parts of the brain. The pineal gland excretes important hormones and neurotransmitters such as melatonin which helps regulate circadian rhythm, as well as, serotonin which is involved in the reward circuitry of the brain. The reptilian brain is believed to be associated with life support and survival. The history and development of the reptilian brain offer us a great deal of insight into our own brains. The reptilian brain is associated with the instinctual region of our minds.
The limbic region, often associated with the emotional mind, generates and controls emotions such as aggression, lust and impulses. The hippocampus and amygdala are two of the major structures in this region. The hippocampus is believed to be essential in the formation of long-term memories. The amygdala aids the hippocampus with memory formation and stimulates cortex with stimuli associated with reward, fear and social functioning. The most outer region is the neocortex which is associated with our analytic mind. Often, behavior can be viewed as a balance, or compromise, between our emotional and analytical minds.
This most outer region of our brain is known as the neocortex which literally means the “new skin,” as it is the newest part of the brain and it covers most of the inner areas of the brain with its crumpled appearance consisting of many ridges and valleys known as sulci and gyri. There are approximately 100 billion nerve cells or neurons in the human cortex (Wadhawan, 2010). Although neurons do have different shapes most of them have a pyramidal shaped central body or nucleus, an axon and a number of branching structures called dendrites. The dendrites are signal receivers and the axon is a signal emitter. A synapse between two neurons is established when the axon of one neuron connects to the dendrite of another neuron. A typical axon can be involved in several thousand synapses. An action potential traveling down the axon of the presynaptic neuron results in the release of neurotransmitters into the synaptic cleft. The neurotransmitters bind to receptors in the postsynaptic membrane and change the probability that the postsynaptic cell will fire its own action potential. Particular sequences of activity can either strengthen or weaken the synapse, changing the strength of the connection between the neurons. Although perhaps oversimplified a common principle during the development and establishment of neuroanatomy is “neurons that fire together wire together,” which form stronger connections between the two neurons. Vernon Mountcastle (1978), one of the fathers of neuroscience, explains that cortical tissue can be functionally divided into vertical units known as columns consisting of neurons that respond in a similar manner to external signals with a particular attribute. This idea is known by most neuroscientists but rarely evident in their research.
Figure 1 Dendritic Tree of a neuron which receives more than 100,000 synaptic inputs (Nelson, 2002)
The cortex is most developed in humans. Although, we do not know fully how the brain works, current research has shown us some of the basis of brain functioning. Most psychologists and cognitive science researchers identify and delineate certain regions of the neocortex which are responsible for certain tasks. For example, the prefrontal cortex is associated with reasoning power and intelligence. When studying the brain people tend to focus on a localizationist approach in which “the goal is to identify the specific locations in the brain where discrete psychological operations occur” (McGill, 2011, p.80).
The processes studied using a localizationist approach vary across the entire spectrum from perception of sensory stimuli to abstract conceptualizations. Many people split the brain into “lobes” where visual information is processed and analyzed in the occipital lobe, auditory information and speech are processed in the temporal lobe, and touch, temperature sensation, smell and taste in the parietal lobes. The frontal lobe is often associated with a great deal of higher level functioning including language, planning, decision making, and judgment.
Then certain areas of these lobes have been delineated to even more specific tasks. For example, expressive language is believed to be found in the left frontal lobe known as Broca’s area and receptive language is found in the left temporoparietal lobe known as Wernicke’s area. These associations have been confirmed by research on cases of individuals that have strokes or incur brain damage to these areas. Other tasks have been determined to take place predominantly in certain hemispheres. For example, recognizing faces and experiencing music is believed to take place in the right hemisphere.
Somewhat in contrast to this localizationist approach, there are global processes which act on specific regions of the brain, but use similar operating principles throughout. That is, sensory receptors, including the eyes, ears and skin convert physical stimuli into neurological signals which are processed in the brain as specific sets of patterns and streams of sequences of information. Although we attempt to quantify the number of senses coming into the brain, in reality, there are an array of sensors consisting of over a million sensors in your eye, a million sensors in your skin and about 30,000 sensors in your cochlea (Hawkins, 2012). We use these sensors to process and predict properties of our environment. The most basic signals are sent to the thalamus and then to respective areas in the primary occipital, temporal or parietal cortexes of the brain. These signals connect to cortical neurons that represent more abstract properties of a given signal. For example, visual signals are compared with recognizable visual features from lines, colors and orientations; songs are broken down into melodies, sounds and various timing, and so on. There is then direct connection across cortical surface areas which create association areas where multimodal mental representations are constructed (Hawkins, 2004). For example, the experience of driving combines our visual processing with the somatosensory senses of our hands on the wheel and foot on the petal, as well as the sounds of our car and the traffic outside, and so on.
Figure 2 Areas of the brain (Wadhawan)
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