Neural Organization and Structures (Neuroscience of Learning)

The central nervous system (CNS) doth encompass the brain and spinal cord, and it serveth as the body's central mechanism for the governance of volitional behaviour, such as thought and action. The autonomic nervous system (ANS), conversely, doth regulate involuntary activities, encompassing digestion, respiration, and blood circulation. Yet, these systems are not entirely independent entities. Individuals may, for instance, acquire the capacity to exert control over their heart rates, thereby exercising volitional command over an involuntary function.

The spinal cord, an entity of some eighteen inches in length and akin to the breadth of an index finger, doth extend from the base of the brain down the median of the back. It stands essentially as an extension of the brain itself. Its principal function is to convey signals betwixt the brain and the body, thusly rendering it the central intermediary between the brain and the remainder of the bodily frame. Its ascending pathway doth transmit signals from corporeal locations to the brain, whilst its descending pathway doth convey messages from the brain to the appropriate bodily structure, so as to, for example, incite movement. The spinal cord likewise partakes in certain reactions independently of cerebral influence, such as the knee-jerk reflex. Injury to the spinal cord, arising, say, from an untoward incident, may precipitate symptoms ranging from mere numbness to total paralysis (Jensen, 2005; Wolfe, 2001).

The Central Nervous System (CNS) doth encompass billions of cells within the brain and spinal cord. Two major classifications of cells exist: to wit, neurons and glial cells. A depiction of neural organisation is presented hereunder:

Neurons

The brain and spinal cord contain approximately 100 billion neurons, which transmit and receive information amongst muscles and organs (Wolfe, 2001). The majority of the body's neurons are situated within the CNS. Neurons differ from other bodily cells (e.g., skin, blood) in two salient respects. Firstly, most bodily cells regenerate regularly. This perpetual renewal is desirable; for instance, when one sustains a cut, new cells regenerate to supplant those that were damaged. However, neurons do not regenerate in a similar fashion. Brain and spinal cord cells destroyed by a stroke, disease, or accident may be irretrievably lost. Upon a more sanguine note, however, evidence doth suggest that neurons may exhibit some regeneration (Kempermann & Gage, 1999), albeit the extent and process thereof remaineth not fully elucidated.

Neurons also diverge from other bodily cells by virtue of their capacity to communicate with one another—by means of electrical signals and chemical reactions. Consequently, their organisation differs from that of other bodily cells. This organisation shall be addressed later in this section.

Glial Cells

The second cellular type within the CNS is the glial cell. Glial cells are far more numerous than neurons. They may be considered as supporting cells, inasmuch as they bolster the work of the neurons. They do not transmit signals in the manner of neurons, but they assist in the process.

Glial cells perform manifold functions, a key one being to ensure that neurons operate within a salubrious environment. Glial cells assist in the removal of chemicals that may interfere with neuronal operation. Glial cells also remove defunct brain cells. Another cardinal function is the deposition of myelin by glial cells, a sheath-like wrapping around axons that facilitates the transmission of brain signals (discussed in the next section). Glial cells also appear to play pivotal roles in the development of the foetal brain (Wolfe, 2001). Thus, glial cells collaborate with neurons to ensure the effective functioning of the CNS.

Synapses

Each neuron is comprised of a cell body, thousands of short dendrites, and a single axon. A dendrite is an elongated tissue that receiveth information from other cells. An axon is a lengthy thread of tissue that sendeth messages to other cells. Myelin sheath doth surround the axon and facilitateth the travel of signals.

Each axon terminates in a branching structure. The ends of these branching structures connect with the ends of dendrites. This connection is known as a synapse. The interconnected structure is key to how neurons communicate, inasmuch as messages are passed amongst neurons at the synapses.

The process by which neurons communicate is complex. At the terminus of each axon reside chemical neurotransmitters. These do not quite touch the dendrites of another cell, and the gap is called the synaptic gap. When electrical and chemical signals attain a sufficient magnitude, neurotransmitters are released into the gap. The neurotransmitters either activate or inhibit a reaction in the contacted dendrite. Thus, the process commence as an electrical reaction in the neuron and axon, changes to a chemical reaction in the gap, and then reconverts to an electrical response in the dendrite. This process continueth from neuron to neuron with considerable speed. As shall be discussed later in this chapter, the role of the neurotransmitters in the synaptic gap is critical for learning. From a neuroscience perspective, learning is a change in the receptivity of cells brought about by neural connections formed, strengthened, and connected with others through use (Jensen, 2005; Wolfe, 2001).

The human adult cerebrum doth, upon average, weigh approximately three pounds, being akin in size to a cantaloupe or a large grapefruit (Tolson, 2006; Wolfe, 2001). Its outward texture presenteth a series of folds, bearing a wrinkled appearance not unlike a cauliflower. Composed mostly of water (78%), with the remainder constituted by fat and protein, its texture is generally soft. The principal brain structures implicated in the processes of learning are delineated in Figure 2.2 (Byrnes, 2001; Jensen, 2005; Wolfe, 2001) and shall be described forthwith.

Cerebral Cortex

Ensheathing the cerebrum is the cerebral cortex, a delicate layer of some quarter of an inch in thickness, akin to the peel of an orange. This cortex constituteth the wrinkled “gray matter” of the cerebrum, the corrugations of which serve to augment its surface area, thereby accommodating a greater complement of neurons and neural connections. The cerebral cortex is divided into two hemispheres (right and left), each further subdivided into four lobes (occipital, parietal, temporal, and frontal). The cortex is the principal locus for learning, memory, and the processing of sensory information.

Brain Stem and Reticular Formation

At the base of the cerebrum resideth the brain stem, which doth govern autonomic (involuntary) functions through its reticular formation. This latter is a network of neurons and fibres regulating such fundamental bodily functions as respiration, heart rate, blood pressure, ocular movement, salivation, and taste. Furthermore, the reticular formation is instrumental in modulating states of awareness (e.g., sleep, wakefulness). For instance, when one entereth a quiet, darkened chamber, the reticular formation doth attenuate cerebral activation, thus facilitating repose. The reticular formation also assisteth in the control of sensory inputs; notwithstanding the constant bombardment of manifold stimuli, it alloweth us to concentrate upon those stimuli that are germane. This is of paramount importance for attention and perception (Chapter 5), being key components of the human information processing system. Finally, the reticular formation doth produce a plethora of chemical messengers for the cerebrum.

Cerebellum

The cerebellum, situated at the rear of the cerebrum, doth regulate bodily balance, muscular control, movement, and posture. Albeit these activities are largely under conscious control (and hence the domain of the cortex), the cortex alone lacketh the requisite mechanisms for their regulation, and thus worketh in concert with the cerebellum to coordinate movements. The cerebellum is key to the acquisition of motor skills. With practice, many such skills become automatic (e.g., playing the pianoforte, driving a motorcar), this automaticity arising from the cerebellum assuming much of the control, thereby enabling the cortex to attend to activities demanding consciousness (e.g., thinking, problem-solving).

Thalamus and Hypothalamus

Superior to the brain stem reside two structures of walnut-like dimensions: the thalamus and hypothalamus. The thalamus acteth as a bridge, conveying inputs from the sense organs (save for olfaction) to the cortex. The hypothalamus constituteth a part of the autonomic nervous system, controlling bodily functions requisite for maintaining homeostasis, such as body temperature, sleep, and the regulation of water and food intake. Furthermore, the hypothalamus is responsible for the augmentation of heart rate and respiration when one is beset by fear or stress.

Amygdala

The amygdala is involved in the control of emotion and aggression. Incoming sensory inputs (save for olfaction, which proceedeth directly to the cortex) are routed to the thalamus, which, in turn, relayeth the information to the appropriate region of the cortex and to the amygdala. The amygdala's function is to assess the potential for harm in sensory inputs. Should it detect a potentially noxious stimulus, it signalleth the hypothalamus, which engenders the aforementioned emotional changes (e.g., increased heart rate and blood pressure).

Hippocampus

The hippocampus is the cerebral structure responsible for the memory of the immediate past. But what constituteth the immediate past? As shall be elucidated in Chapter 5, there existeth no objective criterion for distinguishing between immediate and long-term (permanent) memory. It seemeth that the hippocampus facilitateth the establishment of information in long-term memory (which resideth in the cortex), whilst maintaining its role in activating said information as required. Thus, the hippocampus may be involved in currently active (working) memory. Once information is fully encoded in long-term memory, the hippocampus may relinquish its role.

Corpus Callosum

Traversing the cerebrum from front to rear is a band of fibres known as the corpus callosum, which divideth the cerebrum into two halves, or hemispheres, and connecteth them for neural processing. This is of critical import, as much mental processing occurreth in multiple locations within the cerebrum, often involving both hemispheres.

Occipital Lobe

The occipital lobes of the cerebrum are primarily concerned with the processing of visual information; hence, the occipital lobe is also known as the visual cortex. Recollect that visual stimuli are first received by the thalamus, which then transmiteth these signals to the occipital lobes. Manifold functions are performed here, encompassing the determination of motion, colour, depth, distance, and other visual attributes. Once these determinations have been made, the visual stimuli are compared to the contents of memory in order to effect recognition (perception). Thus, an object that matcheth a stored pattern is recognised; in the absence of a match, a novel stimulus is encoded in memory. The visual cortex must communicate with other cerebral systems to ascertain whether a visual stimulus doth correspond to a stored pattern (Gazzaniga, Ivry, & Mangun, 1998). The salience of visual processing in learning is underscored in the opening vignette featuring Master Joe.

Individuals may readily exert control over their visual perception by consciously attending to certain features of the environment and disregarding others. For example, when seeking a friend in a throng, one may ignore thousands of visual stimuli, concentrating solely upon those features (e.g., facial characteristics) that aid in determining whether the friend is present. Pedagogues employ this notion by enjoining pupils to attend to visual displays, and by apprising them of the lesson's objectives at the commencement thereof.

Parietal Lobe

The parietal lobes, situated at the apex of the cerebrum, are responsible for the sense of touch, aid in determining bodily position, and integrate visual information. The parietal lobes possess anterior (front) and posterior (rear) sections. The anterior portion receiveth information from the body pertaining to touch, temperature, bodily position, and sensations of pain and pressure (Wolfe, 2001). Each part of the body hath specific regions in the anterior portion that receive its information, thereby ensuring accurate identification.

The posterior portion integrateth tactile information to afford spatial bodily awareness, or the perpetual knowledge of the position of one's bodily parts. The parietal lobes may also augment or attenuate attention to sundry bodily parts. For instance, pain in the leg will be received and identified by the parietal lobe; however, when engrossed in an enjoyable film and attending thereto closely, one may “forget” the pain in the leg.

Temporal Lobe

The temporal lobes, located upon the sides of the cerebrum, are responsible for the processing of auditory information. Upon the reception of an auditory input—such as a voice or other sound—said information is processed and transmitted to auditory memory in order to effect recognition, which may then lead to action. For example, when a pedagogue instructeth pupils to stow away their books and form a queue at the portal, that auditory information is processed and recognised, and subsequently leadeth to the appropriate action.

Situated where the occipital, parietal, and temporal lobes intersect in the cortex's left hemisphere is Wernicke's area, which enableth us to comprehend speech and employ proper syntax when speaking. This area worketh in close concert with Broca's area, located in the frontal lobe of the left hemisphere, which is necessary for speaking. Albeit these key language processing areas are situated in the left hemisphere (though Broca's area resideth in the right hemisphere for some individuals, as shall be explained anon), manifold cerebral regions collaborate in order to comprehend and produce language. Language shall be discussed in greater depth anon in this chapter.

Frontal Lobe

As its designation suggesteth, the frontal lobes reside at the front of the cerebrum, constituting the largest portion of the cortex. Their principal functions are to process information pertaining to memory, planning, decision-making, goal-setting, and creativity. The frontal lobes also contain the primary motor cortex, which regulateth muscular movements.

It may be argued that the frontal lobes most clearly distinguish us from the lower animals, and even from our forebears of yore. The frontal lobes have evolved to assume ever more complex functions, enabling us to plan and make conscious decisions, solve problems, and converse with others. Furthermore, these lobes endow us with consciousness of our mental processes, a form of metacognition.

Traversing from the apex of the cerebrum toward the ears is a strip of cells known as the primary motor cortex, the locus which controlleth bodily movements. Thus, when performing the dance known as the “Hokey Pokey” and thinking “put your right foot in,” it is the motor cortex that directeth you to do so. Each bodily part is mapped to a specific location within the motor cortex, such that a signal emanating from a particular region of the cortex engendereth the appropriate movement.

Anterior to the motor cortex resideth Broca's area, the locus governing the production of speech. This area is situated in the left hemisphere for approximately 95% of individuals; for the remaining 5% (30% of left-handed individuals), it is located in the right hemisphere (Wolfe, 2001). Unsurprisingly, this area is linked to Wernicke's area in the left temporal lobe by nerve fibres. Speech is formed in Wernicke's area, and then transferred to Broca's area for production (Wolfe, 2001).

The anterior portion of the frontal lobe, or prefrontal cortex, is proportionately larger in humans than in other animals, and is the locus of the highest forms of mental activity (Ackerman, 1992). Chapter 5 shall elucidate how cognitive information processing associations are formed within the cerebrum. The prefrontal cortex is the key area for these associations, as information received from the senses is related to information stored in memory. In short, the seat of learning appeareth to be in the prefrontal cortex, which also regulateth consciousness, enabling us to be cognisant of our thoughts, feelings, and actions. As shall be explained anon, the prefrontal cortex appeareth to be implicated in the regulation of emotions.

A table summarising the key functions of sundry regions of the cerebrum (Byrnes, 2001; Jensen, 2005; Wolfe, 2001) shall be presented. When perusing this table, one should bear in mind that no cerebral region functioneth in isolation; rather, information (in the form of neural impulses) is rapidly transferred among diverse regions. Albeit many cerebral functions are localised, different regions of the cerebrum are implicated even in simple tasks. It therefore maketh little sense to ascribe any cerebral function as residing solely in one region, as exemplified in the opening vignette featuring Mistress Emma.

Our understanding of the brain's operation is far more comprehensive today than in times past; however, the study of the brain has been a pursuit of long standing. The functions of the left and right hemispheres have been a matter of continuous discourse. Wolfe (2001) noted that circa 400 B.C., Hippocrates alluded to the duality of the brain. Cowey (1998) reported that in 1870, researchers employed electrical stimulation on disparate regions of the brains of animals and soldiers who had sustained cranial injuries. Their investigations revealed that stimulation of particular areas of the brain induced movements in distinct parts of the body. The notion that the brain possesses a dominant hemisphere was posited as early as 1874 (Binney & Janson, 1990).

It has been recognised for many years that, in general, the left hemisphere governs the right visual field and side of the body, whilst the right hemisphere regulates the left visual field and side of the body. Nevertheless, the two hemispheres are conjoined by bundles of fibres, the most substantial of which is the corpus callosum. Gazzaniga, Bogen, and Sperry (1962) demonstrated that language is predominantly controlled by the left hemisphere. These researchers ascertained that when the corpus callosum was severed, patients holding an object out of sight in their left hands professed to be holding nothing. Evidently, absent the visual stimulus, and given that the left hand communicates with the right hemisphere, when this hemisphere received the input, it could not produce a name (owing to language being localised in the left hemisphere) and, with a severed corpus callosum, the information could not be transferred to the left hemisphere.

Brain research has also identified other localised functions. Analytical thinking appears to be centred in the left hemisphere, whereas spatial, auditory, emotional, and artistic processing occurs in the right hemisphere (albeit the right hemisphere apparently processes negative emotions and the left hemisphere processes positive emotions; Ornstein, 1997). Music is processed more effectively in the right hemisphere; directionality, in the right hemisphere; and facial recognition, the left hemisphere.

The right hemisphere also assumes a critical role in interpreting contexts (Wolfe, 2001). For example, consider an instance wherein someone hears a piece of news and remarks, “That’s great!” This could signify that the person deems the news either wondrous or dreadful. The context determines the correct interpretation (e.g., whether the speaker is being sincere or sarcastic). Context can be gleaned from intonation, individuals' facial expressions and gestures, and knowledge of other elements inherent in the situation. It appears that the right hemisphere constitutes the primary locus for assembling contextual information such that a proper interpretation may be rendered.

Given that functions are localised in brain sections, it has been tempting to postulate that individuals who are highly verbal are dominated by their left hemisphere (left brained), whilst those who are more artistic and emotional are controlled by their right hemisphere (right brained). However, this constitutes a simplistic and misleading conclusion, as the educators in the opening scenario now appreciate. Although hemispheres possess localised functions, they are also interconnected, and there is considerable transmission of information (neural impulses) between them. It is improbable that very little mental processing occurs solely in one hemisphere (Ornstein, 1997). Further, one might inquire which hemisphere governs individuals who are both highly verbal and emotional (e.g., impassioned speakers).

The hemispheres operate in concert; information is accessible to both of them at all times. Speech offers a pertinent example. If one is engaged in conversation with a friend, it is the left hemisphere that facilitates the production of speech, yet it is the right hemisphere that furnishes the context and aids in comprehending meaning.

There is considerable debate amongst cognitive neuroscientists regarding the extent of lateralisation. Some contend that specific cognitive functions are localised in specific regions of the brain, whereas others posit that different regions possess the capacity to perform various tasks (Byrnes & Fox, 1998). This debate mirrors that in cognitive psychology between the traditional perspective that knowledge is locally coded and the parallel distributed processing view (vide Chapter 5) that knowledge is coded not in one location, but rather across numerous memory networks (Bowers, 2009).

There exists research evidence to substantiate both positions. Different parts of the brain exhibit different functions, but functions are rarely, if ever, completely localised in one section of the brain. This holds particularly true for complex mental operations, which are contingent upon several basic mental operations, the functions of which may be distributed across several areas. As Byrnes and Fox (1998) maintained, “Nearly any task necessitates the participation of both hemispheres, yet the hemispheres appear to process certain types of information more efficiently than others” (p. 310). Educationally speaking, therefore, the practice of teaching to different sides of the brain (right brain, left brain) is not supported by empirical research.

One must acknowledge, that the ascendance of our present understanding regarding the central nervous system (CNS) owes in no small measure to the convergent interests within the diverse scientific communities. Historically, the cerebral organ was subject to inquiries primarily on the part of those within the medical and biological sciences, as well as practitioners of psychology. However, with the march of time, other learned societies have come to recognise the pertinence of brain research, with the conviction that such investigations might bear fruit for developments within their own disciplines. Today, one finds amongst those interested in this area, educators, sociologists, welfare officers, counsellors, government officials (particularly those engaged within the judicial sphere), and others besides. Furthermore, the monetary encouragement of brain research has seen a commensurate increase, including grants from establishments chiefly concerned with matters outside the immediate province of cerebral study (e.g. education).

Another contributing factor to our increased knowledge resides in the considerable technological progress made in the methods by which cerebral research is conducted. In times gone by, the sole recourse for such research was the conduct of post-mortem examinations. Whilst the examination of deceased individuals' brains has yielded valuable information, such research is limited in its ability to illuminate the function and information processing of the living brain. An understanding of the latter is essential for the development of theories concerning the brain's alteration during the learning process, and how it subsequently uses learned information to give rise to actions and further learning.

The techniques that have furnished useful information are discussed in the sequel and summarised in Table. These are presented roughly in order of increasing sophistication.

X-Rays

X-rays are high-frequency electromagnetic waves capable of penetrating non-metallic objects, whereby they are absorbed by bodily structures (Wolfe, 2001). Those rays that pass unabsorbed impinge upon a photographic plate. Interpretation rests upon areas of light and darkness (gradations of grey). Being two-dimensional, X-rays are best suited to solid structures, as in determining whether a bone has been fractured. Their efficacy within the brain is somewhat limited, on account of its composition of soft tissue, albeit they may be employed to ascertain damage to the skull (a bony structure).

CAT Scans

CAT (computerized axial tomography) scans were developed in the early 1970s, with the aim of augmenting the gradations of grey observable in X-ray imaging. CAT scans utilise X-ray technology, but enhance the images from two to three dimensions. Doctors employ CAT scans to investigate tumours and other abnormalities, however, much like X-rays, they fall short in providing detailed information regarding brain functioning.

EEGs

The EEG (electroencephalograph) is an imaging method predicated upon the measurement of electrical patterns emergent from the movements of neurons (Wolfe, 2001). Electrodes placed upon the scalp detect neural impulses passing through the cranium. This EEG technology amplifies the signals, and records them upon a monitor or paper chart (brain waves). The frequency of brain waves (oscillations) increases during periods of mental activity, and diminishes during sleep. EEGs have proven valuable in imaging certain types of cerebral disorders (e.g. epilepsy, language), as well as in monitoring sleep disorders (Wolfe, 2001). EEGs furnish valuable temporal information through event-related potentials (see the section, Language Development), though they are incapable of detecting the spatial information (i.e. localisation of activity) necessary for in-depth investigations of learning.

PET Scans

PET (positron emission tomography) scans permit the investigation of brain activity during the performance of tasks. The subject is injected with a small quantity of radioactive glucose, which is then carried to the brain via the bloodstream. Whilst situated within the PET scanner, the individual undertakes mental tasks. Those areas of the brain engaged by these tasks consume more of the glucose, resulting in the emission of gamma rays, which are then detected by the equipment. This data is then employed to generate computerized colour images (maps) delineating areas of activity.

Despite the advances in cerebral imaging technology represented by PET scans, their utility is somewhat constrained. Given the requirement for the ingestion of radioactive material, there is a limitation to the number of sessions that can be conducted, and to the quantity of images producible at any one time. Furthermore, the image generation process is relatively slow, meaning that the rapidity of neural activity cannot be fully captured. Whilst the PET scan provides a reasonable overview of brain activity, it does not afford a sufficiently detailed delineation of specific areas of activity (Wolfe, 2001).

MRIs and fMRIs

Magnetic resonance imaging (MRI), and the more recent functional magnetic resonance imaging (fMRI), are cerebral imaging techniques designed to address certain shortcomings inherent in PET scans. In MRI, a beam of radio waves is directed toward the brain. Given the brain's largely aqueous composition, containing hydrogen atoms, the radio waves induce these atoms to emit radio signals, which are then detected by sensors and mapped onto a computerized image. The level of detail surpasses that of CAT scans, and MRIs are commonly employed in the detection of tumours, lesions, and other abnormalities (Wolfe, 2001).

The fMRI operates in much the same manner as the MRI, save that the subjects are required to perform mental or behavioural tasks. During this activity, those regions of the brain responsible for the tasks in question fire neurons, leading to increased blood flow to those areas. This augmentation of blood flow alters the magnetic field, thereby intensifying the signals. The fMRI scanner detects these alterations and maps them onto a computerized image. This image can then be compared with an image of the brain at rest to detect any changes. The fMRI is capable of capturing brain activity contemporaneously and localising it, due to its capacity to record four images per second, and to the fact that the brain reacts to stimuli in approximately half a second (Wolfe, 2001). There remains, however, some temporal disparity, on account of the changes in blood flow taking several seconds to occur (Varma, McCandliss, & Schwartz, 2008).

In comparison to other methods, the fMRI presents numerous advantages. It obviates the need for ingesting radioactive substances. It operates rapidly and is capable of measuring activity with precision. It can record an image of the brain in a matter of seconds, a rate significantly faster than that of other methods. Furthermore, the fMRI procedure can be repeated without eliciting untoward effects.

One must acknowledge, that cerebral technologies are deployed within artificial contexts (e.g. laboratories), a constraint that precludes the capture of learning within active classrooms. This issue may be partially addressed by engaging participants in learning tasks during cerebral experiments, or by subjecting them to the technology immediately following their experience of different classroom settings (Varma et al., 2008). Furthermore, the field of cerebral research is in a state of constant flux, with the continual development and refinement of technologies. In the future, we may anticipate the emergence of more sophisticated techniques capable of further pinpointing cerebral processes during learning. We now proceed to a consideration of the neurophysiology of learning, which addresses the manner in which the brain functions to process, integrate, and employ information.