Cortical Functions

John Stirling

• Publisher: Routledge
• Year: 2020
• ISBN:
  9781000158922
• Edition: 1
• Topic: Psychology
• Subtopic: History & Theory in Psychology
• Index: Psychology

Cortical Functions is a companion to Kevin Silber's series title, The Physiological Basis of Behaviour and concentrates on the cerebral cortex, its structure, connections, functions and dysfunctions. John Stirling includes clinical descriptions and case studies to illustrate various forms of agnosia, aphasia and the split brain syndrome. Methods in neuropsychology are reviewed and other chapters provide comprehensive but straightforward coverage of the role of the brain in language, sensation, perception and movement.

1

The brain and psychological functioning

Introduction

Some history

The localisation of function debate

Distributed control

Summary

Introduction

The adult human brain is the most complicated, wonderful and mysterious structure in the natural world. To the naked eye, its outer surface looks bumpy and creased. Inside, it seems solid, with the consistency of stiff jelly, yet towards the centre, there are four quite large fluid filled cavities. Throughout life (even during deepest sleep) the brain remains active. In relation to the rest of the body, it uses disproportionately large amounts of fuel (glucose). To obtain this fuel, which arrives via the blood supply, it receives about 20% of the entire output of the heart. The brain is responsible for perception and movement. It allows us to think, learn, fear and dream. It weighs just 1200 grams.

In this chapter, I provide a ‘potted’ history of the beginnings of scientific research into the brain, and introduce you to some of the theories (and debates) that have surfaced as our understanding of this incredible biological machine has developed. The background I provide will help you to understand the context in which psychologists and other scientists have set about doing brain research.

Some history

Historical records from the Middle East suggest that the importance of the brain as a control centre was first considered at least 5000 years ago, although for many the heart was viewed as the organ of thinking and other mental processes. The ancient Greeks also debated the relative merits of heart and brain. Hippocrates and Plato both had some understanding of brain structure, and attributed various aspects of behaviour to it. Hippocrates warned against probing a wound in the brain in case it might lead to paralysis in the opposite side of the body. In Rome, the physician Galen, who spent a number of years working as a surgeon to gladiators, was also only too well aware of the effects that brain damage could have on behaviour.

However, the knowledge and understanding of these early writers was lost or forgotten for the next 1500 years or so of European history. Those with any interest in the brain concentrated on misguided attempts to find the location of the soul. Their search focused on easily identifiable brain structures including the pineal gland and the corpus callosum. Today, these same structures are known to be involved in the control of bodily rhythms and communication between the two sides of the brain respectively.

The localisation of function debate

The early researchers were also interested in the concept of localisation of function, although they concentrated their search within the fluid cavities (known as ventricles) mentioned earlier rather than the surrounding brain tissue. The basic idea of localisation of function is that different regions of the brain are involved in specific and separate aspects of psychological functioning. This idea certainly interested both Gall and his student Spurzheim, whose work represents the starting point of what we might call the modern era of brain–behaviour research. Gall (1785–1828) readily accepted that the brain, rather than the heart, was the control centre for mental function, and with Spurzheim, the two made many important discoveries about the anatomy of the brain and spinal cord.

The rise and fall of phrenology

Gall thought that the brain consisted of 27 compartments or regional faculties. These ranged from common-sense ones such as language and perception to ambiguous and obscure ones including hope and self-esteem. According to Gall, the more a person used his or her faculties, the bigger the brain in that region grew, causing the shape of the skull to be distorted. Thus was born the ‘science’ of phrenology, which claimed to be able to describe an individual’s personality and other ‘faculties’ on the basis of the physical size and shape of the skull.

Interest in phrenology gradually spread, receiving royal support when Queen Victoria had her children’s heads measured and analysed. Gall and Spurzheim collected thousands of measurements, including a series taken from the skulls of 25 murderers, and even from an amorous widow who was described as having prominent features (bumps) behind her ears! Each observation simply confirmed the general theory, except that the number of faculties crept up to 35!

Doubts about phrenology first arose when it became apparent that the shape of the skull bore little relationship to the shape of the underlying brain. Obviously at the time, Gall and Spurzheim had no way of measuring the internal brain structure of living people, save for those rare instances of individuals surviving (and often not for very long) open head injuries. Actually, records show that Gall had access to a small number of such cases, and he is credited with providing the first full account of brain damage linked to loss of language (aphasia). Unfortunately, he seemed to regard these cases as being of only anecdotal interest, preferring instead to accumulate more and more measurements from members of the general population which ‘confirmed’ his ideas.

The French scientist Pierre Flourens provided the evidence which led people to begin to question the value of phrenology. Working with animals, he developed the technique of surgically removing small areas of brain tissue, and, after a period of recovery, observing the effects of the surgery on behaviour. (We now refer to these procedures as lesion and ablation, and they are described more extensively in Chapter 3). Using these techniques he was able to show that the brain region that Gall had thought responsible for the amorous behaviour of his famous widow actually appeared to co-ordinate balance!

Flourens’ research led him to argue that the degree of behavioural impairment was as much linked to the amount of damage as to its location. This view undermines the principle of localisation of function that Gall and Spurzheim had promoted. Flourens also believed that undamaged regions could take over the responsibilities of damaged ones. This idea gave rise to the popular (but mistaken) belief that people only use a small proportion their brains, keeping other areas in reserve for learning new skills or replacing damaged areas.

Interest in aphasia

Despite Flourens’ lack of enthusiasm for localisation of function, interest in it grew with the publication of a series of case-studies of aphasia. French researchers Bouillaud and Dax independently described patients they had seen who had lost the use of language after brain damage to the left side. These patients often became paralysed in the right side of their bodies too, despite no apparent loss in intelligence.

In 1861, Paul Broca described the case of ‘Tan’, so-called because this had become the only sound he could utter. However, he could understand speech well and could, for example, follow complicated instructions. In fact, in most other respects, he seemed normal, except that he too was paralysed on his right side. Broca proposed that Tan had suffered damage to the same area of brain (the left-frontal region, meaning on the left side towards the front) earlier identified as crucial for language production by Gall. When Tan died from an unrelated disease later that year, Broca conducted a post-mortem on his brain, and confirmed that he had indeed incurred left-frontal brain damage from a stroke.

Within two years, Broca had collected post-mortem data on eight similar cases. This research led him to conclude that language production depends on intact left-frontal function, and that, in more general terms, the two sides of the brain seem to control the opposite sides of the body. (In fact, neither of these ideas was new. The relationship of one side of the brain to the opposite side of the body had been described by Galen almost 2000 years earlier, and the link between left-sided damage and aphasia had first been proposed by Dax and Bouillaud in the 1830s.) Nevertheless, Broca seemed to gain the credit, and the region of brain (part of the left frontal cortex) he described is now known as Broca’s area.

Soon, other regions of cortex were identified as being important for other aspects of language. In 1874, Carl Wernicke described two additional forms of aphasia, distinct from Broca’s type. In fluent aphasia, the patient can speak at a normal rate, but what is said usually makes little sense. In conduction aphasia, the patient seems to understand what is said to them but is unaware of what they themselves are saying! Fluent aphasia occurred in individuals with damage to a region of their left temporal lobe (the brain area roughly behind and above the ear). In conduction aphasia there was evidence of damage to the connections between this region (now known as Wernicke’s area) and Broca’s area. Thus, within a few years, three different brain regions, all on the left side, had been identified as crucial for normal language. In 1892, Dejerine identified the cortical area (these days called the angular gyrus) related to the loss of the ability to read (known as alexia), and the localisation of function concept gained considerably in credibility.

Progress exercise

Match up the names with the ‘ideas’, and write one sentence describing the idea itself:

Flourens	anti-localisation
Gall	left-brain language
Galen	27 faculties
Dax	brain damage and loss of function

Mass action and equipotentiality

Despite the evidence presented in the previous section, it would be misleading to suggest that all psychologists since that time have accepted without question the idea of localisation. Several alternative theories have been proposed this century, including Lashley’s principles of mass action (that the entire cortex is involved in all functions), and equipotentiality (that each cortical region can assume control for any given behaviour).

Lashley’s ideas can be traced back to the work of Flourens that I mentioned earlier, and like him, Lashley used lesion and ablation techniques, and worked exclusively with animals. Many of his studies measured the effects of brain lesions on speed of maze learning in rodents. He would remove a small region of brain, then, following a period of recovery, see how quickly the animal could learn to find a food pellet at the end of a maze. On the basis of many such trials, Lashley concluded that the amount of lesioned brain tissue rather than its location best predicted how poorly the rat would do in the maze, supporting his idea of mass action.

However, his findings could also be used to support localisation of function. Think for a moment about the information a rat might use to run the maze and find the food. Presumably this could include visual information, tactile information and smell, in addition to any more sophisticated concepts such as sense of direction, distance travelled and so on. Indeed, effective maze learning probably depends on the integration of all this information. When Lashley lesioned’ different bits of brain, he might have interfered with the animal’s tactile skills or sense of smell, whilst leaving other functions intact. The animal could still learn the maze using the ‘localised’ functions that remained, although not as quickly as before.

Sound experimental support for Lashley’s ideas has been hard to come by, and it is probably helpful to know that most psychologists continue to favour some form of localisation. Indeed, at present, the main questions in this area of psychology are less to do with whether or not t...

Table of contents

• Cover
• Half Title
• Series Page
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• List of illustrations
• Acknowledgments
• 1 The brain and psychological functioning
• 2 The structure of the brain
• 3 Methods in neuropsychology
• 4 Lateralisation
• 5 Sensory and motor function
• 6 Language and the brain
• 7 Visual mechanisms and perception
• 8 Three research reports
• 9 Study aids
• Glossary
• References
• Index