Clinical Neuropsychology
1 Introduction to Clinical Neuropsychology
A Definition of Clinical Neuropsychology and Its Aims
The study of human behaviors, emotions, and thoughts and how they relate to the
brain, particularly the damaged brain, is the subject matter of clinical neuropsychology.
Clinical neuropsychology has both applied and academic aims. Applied aims include
learning more about neurological disorders and diseases so that we can more accurately
and usefully diagnose, treat, and rehabilitate people who suffer such disorders and, along
with other disciplines, ultimately find ways to prevent their occurrence. The primary
academic aim is to learn more about how the undamaged or “normal” human brain and mind
work by carrying out experiments, usually in the form of cognitive tests, on brain-damaged
people.
Relationship of Clinical Neuropsychology to Other Disciplines
The main ones can best be conceptualized as a continuum with the brain at one end
(neurology) and the mind at the other (cognitive psychology). Neurology is the study of the
medical aspects of CNS disorders and treatments. Compared with neuropsychologists,
neurologists tend to be more concerned with clinical symptoms and signs as indications of
underlying neuropathology in the brain, spinal cord, and peripheral nervous system and less
concerned with the details of the higher behaviors and cognitions mediated by the brain and
how the detailed study of their breakdown can inform us about normal higher cognitive
processes.
The aim of cognitive psychology is to understand the workings of the human mind
by analyzing the higher cognitive functions and their components. Participants in cognitive
psychology experiments are unimpaired people (usually undergraduate university students)
rather than brain-damaged patients, and cognitive psychologists have developed many
important experimental paradigms that allow measurement of minute differences in cognitive
performance under controlled conditions, from which inferences can be made about the
cognitive processes underlying the behaviors.
Cognitive neuropsychology is a hybrid of cognitive psychology and clinical
neuropsychology. It concentrates on the detailed analysis of higher cognitive functions, often
using similar paradigms to those used in cognitive psychology, but it studies brain-damaged
patients rather than “normals”. In their hypotheses and analyses of deficits and their
implications for the normal functioning of the brain, cognitive neuropsychologists, although
certainly not ignoring the brain entirely, tend to be less interested than clinical
neuropsychologists in where the damage is and how it might be related to the impairment.
Similarly, they are not interested in brain pathology, disease, and treatment on their own per
se, but only as a means to the end of understanding the workings of the normal mind.
Thus, clinical neuropsychology positions itself between neurology and cognitive
neuropsychology. It has a neurological interest in brain pathology and the resulting
symptoms and a psychological interest in the analysis of higher cognitive functions, both to
understand the workings of the normal mind and to develop better rehabilitation methods for
patients. In practice, disciplines overlap considerably, and many practitioners and
researchers straddle two or more of these.
,Functional Neuroanatomy
Gross Structure of the Brain
The brain has three major divisions: the cerebral hemispheres, the cerebellum, and
the brain stem. The brain stem, an upward extension of the spinal cord, consists of four
parts: the medulla oblongata, pons, midbrain, and diencephalon. It is the life-support part
of the brain as it controls respiration, cardiovascular function, and gastrointestinal function. It
also contains the nuclei for the cranial nerves connected with the special senses, but it is not
directly concerned with higher cognitive function. The cerebellar hemispheres are paired
structures at the base of the cerebral hemispheres and are concerned mainly with motor
coordination, muscle tone, and balance.
The cerebral hemispheres are covered by a highly convoluted layer of nerve cells
called the cerebral cortex, or gray matter. The “hills” of the cortex are called gyri and the
“valleys” are called sulci. The axons or fiber tracts that connect the nerve cells to the rest of
the brain form a layer directly below the cortex called the white matter. The two
hemispheres are separated by the longitudinal fissure, a deep groove that runs from the
anterior frontal lobes to the posterior occipital lobes. The other main fissures are the central
(or rolandic) fissure or sulcus, which separates the frontal from the parietal lobe, and the
lateral (or sylvian) fissure or sulcus, which separates the temporal lobe from the frontal
and parietal lobes. A tough band of interhemispheric fibers called the corpus callosum forms
the major functional connection between the two hemispheres. Within each hemisphere,
fiber tracts connect different parts of the hemisphere.
The ascending reticular formation (RF) controls the overall arousal level of the
cortex. The RF is a diffuse system of multisynaptic neuron chains traveling up through the
brain stem. All the major sensory pathways send impulses via collateral axons to the RF,
which relays them to a group of nuclei in the thalamus, paired grey matter structures deep
in the brain on either side of the midline at the upper end of the brain stem. The thalamus
serves as a relay center for motor pathways, many sensory pathways, and the RF. On
reaching the thalamus, the impulses are relayed to the cerebral cortex, where they influence
the level of mental alertness or sleep.
Within the brain lies the limbic system, which includes the hippocampus and
amygdala; the cingulate gyrus; and some deep, midline structures in the brain, including the
mamillary bodies. The limbic system is involved in emotion, motivation, and memory.
The brain has three coverings, called the meninges (example of condition to
meninges: meningitis). The outermost thick, tough, covering is called the dura mater (“tough
mother”), which adheres to the inner surface of the skull. The delicate, filamentous middle
membrane, called the arachnoid mater (“spider mother”), is attached by cobweb-like
strands of tissue to the fine pia mater (“little mother”), which adheres closely to the cortex.
The subarachnoid space lies between the arachnoid mater and the pia mater and is filled
with cerebrospinal fluid (CSF). Blood vessels also lie within the subarachnoid space and
dip down in the sulci to supply deeper parts of the brain.
The ventricles are lakes of CSF located deep within the hemispheres (example of
condition: hydrocephalus).
The cerebrovascular system involves in simple terms two pairs of cerebral arteries:
the internal carotid arteries, which supply the anterior parts of the brain, and the vertebral
arteries, which supply the posterior parts of the brain. The two internal carotid arteries enter
the skull and ascend on either side of the optic chiasm, where each artery branches to form
the anterior cerebral arteries (ACA) (travel medially and lower surfaces of frontal, parietal
lobes and corpus callosum) and middle cerebral arteries (MCA) (travel laterally; supplies
,75%< of blood supply to the cerebral hemispheres), one set in each hemisphere. The paired
vertebral arteries enter the skull at the point where the spinal cord becomes continuous with
the brain stem and join to form the single basilar artery on the undersurface of the
brainstem; the basilar artery then divides to form paired posterior cerebral arteries, which
supply the occipital lobes and parts of the medial and inferior surfaces of the temporal lobes,
including the hippocampus. The internal carotid and vertebral arterial systems are linked at
the base of the brain by a single anterior communicating artery and two posterior
communicating arteries, forming a ring of vessels lying in the subarachnoid space, called
the Circle of Willis (example of condition: aneurysm -> which could in turn cause a
subarachnoid hemorrhage).
Cerebral Cortex
By dividing the cerebral hemispheres into primary, secondary, and tertiary cortical
zones, the anatomical-functional relationships of the cortex can be conceptualized. The
parietal, temporal, and occipital lobes lying behind the central sulcus constitute the posterior
cortex and are involved mainly in a person’s awareness of what is happening in the world.
Each of these lobes can be divided into three zones. The primary zones are primary
projection areas in which incoming sensory information is projected to sense-modality-
specific neurons. Each side of the body is mapped topographically onto the primary sensory
strip of the opposite (contralateral) hemisphere. Thus, a touch on the index finger of the right
hand is projected to specific neurons in the primary sensory cortex of the left parietal lobe
(the postcentral gyrus lying directly behind the central sulcus). The position of the finger
would be projected to other specific neurons in the primary zone. The primary zone of the
temporal lobes is concerned with sounds, and different frequencies are represented in
different parts of the primary zone. Similarly, the primary zone of the occipital lobes
represents specific parts of the visual field. Damage to specific areas of the primary cortex
results in highly specific deficits of sensation in the topographically related body part or
sense organ.
The secondary zones (or “association cortex”) lie adjacent to the primary zones.
The neurons in these zones, unlike those in the primary zones, do not have a direct
topographic relationship with sensory information relayed from a particular body part or
sense organ. Instead, they receive the modality-specific information from their primary cortex
and integrate it into meaningful wholes. Thus, the secondary cortex is concerned with
perception and meaning within a single-sense modality. Damage to parts of the secondary
cortex can therefore result in an inability to perceive or comprehend what one is touching or
hearing or seeing, depending on whether the damage is in the parietal, temporal, or occipital
secondary zones.
The tertiary zones lie at the inner borders of each lobe so that the parietal, temporal,
and occipital tertiary zones overlap. At this level, modality specificity disappears, and
integration of information across sense modalities occurs. Damage to the tertiary zones can
lead to complex higher cognitive disorders that involve transmodal integration (e.g., writing to
dictation). The tertiary zones also have links with the limbic system, which is involved in
emotion and memory; therefore, disorders resulting from damage to the tertiary cortex may
also involve abnormal emotional components.
The frontal lobes lie anterior to the central sulcus and are concerned mainly with
acting on knowledge relayed to the posterior part of the cerebral cortex from the outside
world. The frontal lobes can also be divided into three zones. The primary zone, or motor
strip, is on the precentral gyrus, immediately anterior to the central sulcus, and parallels the
, sensory strip in that each side of the body is mapped topographically (like a person hanging
upside down) onto the primary motor strip of the opposite (contralateral) hemisphere. The
secondary zone (association cortex), also called the premotor cortex, mediates the
organization of motor patterns, such as riding a bicycle. The tertiary zone, also called the
prefrontal cortex, is a large area situated at the anterior pole of the brain; it includes both
the lateral cortex and the basomedial (or orbitomedial) cortex, which lies between the two
hemispheres and extends to the underside of the frontal lobes above the eyes. The tertiary
cortex is involved in executive functions, including planning, organization, and abstract
thinking. Because they also have rich connections with the limbic system, the prefrontal
lobes are intimately involved with mood, motivation, and emotion, and damage to them can
result in many and varied impairments involving the interactions of motivational and
emotional states and executive functions.
All three posterior lobes (in each hemisphere; parietal, temporal, occipital) are
involved in the awareness, perception, and integration of information from the outside world,
although their connections with the limbic system ensure that the way the world is
experienced is influenced by the individual’s mood, motivation, and past experiences.
Generally, the parietal lobe is involved in functions involving tactile sensations, position
sense, and spatial relations. The left parietal lobe has a bias toward sequential and logical
spatial abilities, such as perceiving the details within a spatial pattern, whereas the right
parietal lobe is more involved with the holistic appreciation of spatial information.
The temporal lobes are concerned primarily with auditory and olfactory abilities, but
they are involved in integrating visual perceptions with other sensory information. They also
mediate some memory functions, especially those involved in new learning. Their intimate
connections with the hippocampus, a part of the limbic system, allow the integration of
emotion and motivation with the sensory information relayed from the outside world to the
posterior lobes of the hemispheres. The left temporal lobe is concerned more with verbal
and sequential functions; it includes the language comprehension area and is involved in
new verbal learning and memory. The right temporal lobe tends to be more concerned with
nonverbal functions, such as the interpretation of emotional voice tone and emotional facial
expression and the appreciation of music and non-language sounds.
The occipital lobes are the visual lobes, and they mediate sight, visual perception,
and visual knowledge. A patient with a large lesion of the right occipital lobe may have a
complete left-visual-field defect (loss of vision) in the visual fields of both eyes (called a
homonymous hemianopia), and a patient with bilateral lesions of the primary visual cortex at
the very pole of the occipital lobes will be unable to see although his eyes function normally:
cortical blindness. Visual-field defects can also occur if the visual pathways are damaged
at other points. A lesion in the right temporal lobe that damages the optic radiation as it
travels from the optic chiasma to the occipital cortex will result in a visual-field defect in the
upper left quadrant of both eyes. A lesion of the right parietal lobe that damages the optic
tract will result in a visual-field defect in the lower left quadrant of both eyes. Lesions of the
occipital secondary or association cortex can result in a number of strange disorders,
particularly when the lesions are bilateral. For example, a patient with bilateral medial
occipital lobe lesions can see and describe the form of objects, but is unable to recognize
what it is he is seeing: visual agnosia. Again, there is some functional division between the
occipital lobes of the left and right hemispheres, with the left occipital lobe being more
concerned with visual language functions such as reading, and the right occipital lobe being
more concerned with visually judging the orientation of lines or objects in space.
