Cartwright, Evolution and Human Behaviour, Palgrave 2016
Chapter 10 Supplementary
Contents of this section
10.1 Darwin on the emotions
10.2 Facial expressions: humans and primates
10.3 Brain Structure
10.3.1 The central nervous system (CNS)
10.3.2 The two hemispheres
10.3.3 The Amygdala
10.3.4 Mirror neurons and the understanding of emotions
10.1 Darwin on the emotions
Darwin tackles the emergence of human emotions by reference to three principles (Darwin,
1872):
1. Serviceable habits. By this he meant that the expression of emotions originated in
movements that were once useful –such as raising the eyebrows when surprised to
allow more light (and so more information) to enter the eyes. Or the mouth open
threat posture of primates as a possible relic of an attacking position. Darwin
suggested that through time these became fixed as a corollary to an emotion even if
the action no longer served any function
2. Antithesis. Darwin thought that if a certain frame of mind produced a reaction (such
as accounted for by serviceable habits) then the opposite frame of mind might excite
an action that is opposite but not necessarily of any use. As an example Darwin cited
astonishment. A normal relaxed and un-astonished individual stands with arms
relaxed at his side, palms concealed and fingers close together. An astonished
reaction, claimed Darwin, is one where both hands are forced forwards palms
outwards and fingers apart. This reaction does not serve any function but is simply the
opposite of a state of non –astonishment. Similarly, to avert one’s gaze is a sign of
social submission which may be the opposite of a direct gaze which is a sign of threat.
3. Direct action of the nervous system. Reflecting the immature state of physiology in
his day, Darwin thought that some reactions were simply the result of nervous forces
(such as trembling in great fear of joy or excitement) acting on the body against the
will and to no functional purpose.
Cartwright, Evolution and Human Behaviour, Palgrave 2016
In this book, Darwin was keen to stress above all two main points: the continuity between
humans and other animals, and the universal character of human emotional expression. These
two points were instrumental to his broader aim of showing that mankind had a single origin
somewhere in Africa ( and was not a product of special creation or the separate evolution of
different species giving rise to different races), and that man had evolved from more humble
life forms. As he wrote towards the end of The Expression of the Emotions in Man and the
Animals:
“I have endeavoured to show in considerable detail that all the chief expressions exhibited by
man are the same throughout the world. This fact is interesting as it affords a new argument
in favour of the several races being descended from a single branch…before the period at
which the races diverged from each other” (p. 355)
So for Darwin, facial expressions were universal, innate and inherited from our primate
ancestors. Fear, for example, may cause our skin to prickle and our hair to stand on end (“like
the fretful porcupine”) since this may have helped our mammalian ancestors by making them
appear larger, but for modern humans it was not of much use anymore. Darwin thought that
showing emotions to be non-functional helped his more general arguments in favour of the
descent of humans. For if emotions were useless relics then this served as a counterargument
against Creationist who argued that the fine design of our emotional system was a sign of
God’s wise handiwork.
10.2 Facial expressions: humans and primates
Another way of testing for similarities between humans and other primates is to make
observations on young infants and young chimpanzees in terms of their social development.
One of the most widely used assessments is called the Neonatal Behavioural Assessment
Scale (NBAS). This incorporates observations on how infants orient themselves to objects,
their use of resources to regulate their own behaviour, the range of their emotional arousal
and signs of stress. Kim Bard (2005) has applied this types of analysis to various groups of
human infants and chimpanzees. Some of the chimps were raised in the presence of humans
and some raised primarily by their chimp mothers. Bard found that young humans and
chimps have much in common. Very young chimpanzees, for example, give smiles and
positive vocalisations to familiar faces and even show signs of anger.
10.3 Brain Structure
10.3.1 The central nervous system (CNS)
Cartwright, Evolution and Human Behaviour, Palgrave 2016
The nervous system of the human body is divided into central and peripheral divisions. The
central nervous system consists of the brain and spinal cord. The brain (or cerebrum)
consists of left and right central hemispheres joined together by a bundle of fibres known as
the corpus callomen (see Figure 10.2). The collection of nerves that connects the central
nervous system with the periphery of the body (skin and visceral organs) is called the
peripheral nervous system. Like all living tissue the nervous system is made up of cells, in
this case neurons and glial cells. Neurons are the crucial cells for communication and consist
of a central cell body (containing all the main machinery found in most cells such as a
nucleus, mitochondria and other organelles), output fibres known as axons and input fibres
known as dendrites.
Figure 10.1 The structure of neurons. Neurons are nerve cells found in the brain that process
and transmit information. One estimate puts the number of neurons in the human brain as
high as 10 12 (a trillion) with each neuron having thousands of synaptic connections
(Thompson, 2000).
Cartwright, Evolution and Human Behaviour, Palgrave 2016
Neurons interconnect to form circuits. The typical connection is an axon making contact with
the dendrite of another cell at a junction point known as a synapse.
The average neuron sends impulses to about 1,000 other neurons. Neurons are divided into
motor neurons that conduct impulses towards muscles, sensory neurons that respond to
sensory inputs such as light, and interneurons that act as “go-betweens” or bridges between
other neurons.
Slicing through the brain reveals areas of dark (grey) and pale (white) material. The grey
matter takes its colour from the tight packing of neuron cell bodies. The white matter takes its
hue from the myelin sheaths that insulate the fibres stemming from the grey matter.
The brain is divided into three main regions based on their location in the embryo. These are:
the hindbrain, midbrain and forebrain (Figure 10.2). Box 10.1 shows a further breakdown of
cerebral components.
Figure 10.2 The forebrain, midbrain and hindbrain
Cartwright, Evolution and Human Behaviour, Palgrave 2016
Cartwright, Evolution and Human Behaviour, Palgrave 2016
………….Box 10.1 ……………..
THE CENTRAL NERVOUS SYSTEM
BRAIN
The
Hindbrain
The
Midbrain
The Forebrain
Medulla.
Structure
immediately
above the
spinal cord.
Controls life
support
functions (for
example,
breathing and
heartbeat)
Reticular
formation.
Phylogeneti
cally one of
the oldest
parts of the
brain.
Involved in
stereotypica
l actions
such as
walking and
sleeping
Limbic system. Mostly located beneath cerebral
cortex. Associated with learning, memory and emotion
The Pons.
Found in the
front portion
of the brain
stem. Many
ascending
and
descending
fibres run
though the
pons. The
pons
regulates
motor
messages
travelling
downward
from the
higher brain
to the
Hippocampus. A small part of the limbic system found
in each lobe. Involved in memory.
Amygdala. An almond shaped nucleus in each of the
temporal lobes. Involved in the processing of emotion.
Hypothalamus. Controls a range of autonomic
functions, for example, hunger, thirst, body
temperature, wakefulness and sleep. Linked to
hormonal system
Corpus Callosum. Provides connection between the
two halves of the brain.
Thalamus. Two egg-shaped structures, one in each
hemisphere, lying near top of brain. Relays information
from the senses to higher parts of the brain.
SPINAL
CORD
Cartwright, Evolution and Human Behaviour, Palgrave 2016
cerebellum
Cerebellum.
Lies just
above the
medulla.
Coordinates
fine motor
control.
Stores
repetitive
procedures
Reticular
formation
(lower).
Controls
waking and
sleep
Cerebrum. In humans contains about 70% of all
neurons.
Frontal lobes. Portion of
each hemisphere from front
of cerebrum to central
sulcus. Involved in emotion
and language
Parietal lobes. Top of each
hemisphere from central
sulcus to occipital lobes
Occipital lobes. Rear
portion of each hemisphere.
Contains area involved in
vision
Temporal lobes. Portion of
cerebrum on either side of
head. Involved in emotion,
vision and language
The Neocortex. The
most recent part of the
cerebral cortex. Other
parts of the cortex called
allocortex. In humans
the neocortex makes up
90% of the entire
cerebral cortex. Outer
payer of entire
cerebrum.
A late addition to the
brain in evolutionary
terms. About 2 – 4 mm
thick and up to six
layers. Involved with
higher brain functions
such as sensory
perception, conscious
thought and language. A
highly folded structure,
it comprises about 75%
of the brain volume.
Contains about 20% of
all the neurons of the
brain.
……………………………..end of box……………………………………
Cartwright, Evolution and Human Behaviour, Palgrave 2016
Of these components the most important division for humans is the forebrain, and the most
evolutionary “advanced” or recent part of this is the cerebral cortex about 90 per cent of
which is called the neocortex. The neocortex (sometimes called isocortex) can be identified
by the fact that it is laminated intio six layers; the rest of the cortext (or allocortex) has a
variable number of layers. The cerebral cortex plays a crucial role in thinking and language.
It is made up of grey matter and other grey matter areas outside of it, such as the basal
ganglia, the amygdale and even the cortex covering the cerebellum in the hindbrain, are
referred to as “sub cortical”. The cerebral cortex consists of a sheet of cells about 4mm thick
that forms a mantle over the cerebral hemispheres following the ridges and grooves (sulci) of
the convoluted surface of the brain below. The cortex is divided into four spatially distinct
lobes by anatomists – although they are probably not separate structures- called the frontal,
temporal, parietal and occipital lobes.
10.3.2 The two hemispheres
The fact that the brain consists of two hemispheres joined by a narrow bridge is familiar
knowledge. Structurally, at first glance, the left and right sides of the brain appear to be
mirror images of each other. Yet it is now well established that they perform quite different
functions; a phenomenon known as lateralisation. Evidence for this asymmetrical
distribution of functions across the two hemispheres comes from a variety of sources and
approaches. One technique is to rely upon the fact that visual information from left and right
fields of vision is sent to the opposite side of the brain (hence left field of vision to right side
of the brain). In one typical experiment to probe the different functions of the two halves of
the brain, Spence, Shairo and Zaidel (1996) presented emotionally disturbing information to
each hemisphere. They found that information presented to the right hemisphere produced
greater changes in heart rate and blood pressure than the same information presented to the
left hemisphere. They interpreted this as indicating that the right hemisphere plays a greater
role in the processing of emotion than the left.
Studies on patients with a damaged hemisphere are also instructive. Generally it has been
found that damage to the left hemisphere has a major impact on linguistic ability but damage
to the right a much smaller impact, suggesting that linguistic ability resides primarily (but not
exclusively) in the left hemisphere. But studies such as these on the abilities of subjects with
damaged brains are made difficult by the fact that the two hemispheres pass information back
and forth through a connecting bundle of fibres known as the corpus callosum (see Figure
10.2). This has meant that researchers have typically had to look for quick responses before
each side can inform the other what is going on. However, as a treatment for epilepsy, some
patients have undergone surgery to sever the corpus callosum, leaving each side of the brain
to operate independently. Studies on these patients have been illuminating. They show, for
Cartwright, Evolution and Human Behaviour, Palgrave 2016
example, that for these subjects emotional stimuli are only processed accurately when the
information is accessed by the right side of the brain.
More recent research has revealed further layers of complexity. It now seems that the lateral
bias in the recognition of emotions might depend upon whether the emotions are positive or
negative. It looks like the right side is involved with the recognition and processing of
unpleasant emotions but the left side has a role in the experience of more positive and
welcome emotions. This is called the valence hypothesis (see Schiff and Lamon, 1994,
Springer and Deutch, 1998, and Workman, L. , Peters, S., and Taylor, S., 2000)
Figure 10.3 Lateralisation of some brain functions
Left hemisphere
Right Hemisphere
Language
Spatial reasoning
Computing
Face recognition
Logical reasoning
Music
10.3.3 The Amygdala
Figure 10.4 Location of the amygdala, the hippocampus and the insula.
Cartwright, Evolution and Human Behaviour, Palgrave 2016
The fact that each hemisphere is involved in some way in emotional processing is indicated
by the presence in both halves of the brain of a small, almond-shaped organ called the
amygdala (plural amygdalae). The amygdala is part of the brain’s limbic system. Patients
with damage to both amygdalae are quite rare but experiments on rats and monkeys have
shown the importance of this organ in the mammalian emotional system. As early as 1939,
for example, Heinrich Kluver and Paul Bucy found that surgical disruption to the temporal
lobes (a part of the brain that controls the amygdalae) of monkeys caused them to show less
fear and behave less aggressively. More generally it seems that damage to the amygdalae of
primates greatly compromises their ability to recognise the motivational and reward value of
stimuli. Typically, they will attempt to copulate with individuals of other species
(noncospecifics) and attempt to eat foodstuffs normally found unattractive. The end state of
the monkeys was termed placidity. So well established is this effect it is sometimes called
social-emotional agnosia (that is, lack of knowledge) or the Kluver-Bucy sundrome (see
also Weiskrantz, 1956) For a short time in the United States this led to a series of
amygdalotomies carried out by “psycho surgeons” on criminals with the aim of reducing their
fear and anger. More recently, Joseph LeDoux (1997) has shown that the surgical removal of
the amygdale in laboratory rats greatly reduces their rapid response to a fearful situation.
Supplementing this there is now considerable evidence that humans who have suffered
damage to their amygdalae have impaired recognition of fear and anger. Damasio (2000)
describes the remarkable case of a young woman who suffered from Urbach-Wiethe’s disease
whereby calcium deposits in her brain gradually destroyed both her amygdalae. In treating
this patient Damasio found that she behaved in a very friendly manner towards all the clinical
staff, showed little reserve, and, interestingly, ( as Damsio’s co-worker Ralph Adolph found)
seemed unable to recognise the emotion of fear in another person’s face. In addition, despite
having good drawing skills, she was unable to draw a fearful face even though faces
displaying other emotions caused no problems.
The amygdala is also involved in triggering the release of stress hormones such as adrenalin
and the glucocorticoids from the adrenal glands (structures that lie just above the kidneys). In
Cartwright, Evolution and Human Behaviour, Palgrave 2016
the case of adrenalin, this acts upon the muscles to prepare them for action. James McGaugh
and colleagues have shown that such hormones also act on memory function. This of course
makes good adaptive sense: it is important to remember those encounters that caused stress
and how we dealt with them (McGaugh et al, 1999)
The low roads and high roads of fear
It is now well established that the amygdalae send signals to virtually every other area of the
brain and receives inputs from both the lower thalamic region of the brain and more complex
information from the higher cortical centres. These findings have led LeDoux to suggest that
there are two types of circuitry involved in fear. One is a quick and dirty or “low road”
response (thalamus-amygdala) circuit that by passes the cortex but produces a rapid
unthinking and instinctive reaction. The other response proposed by LeDoux is a slower more
considered “high road” response (thalamus to cortex to amygdale) that produces a cognitive
evaluation of the threat and allows us to response appropriately. As an illustration, imagine
you are walking home alone one dark night and you sense a sudden movement behind you.
On hearing the noise behind, you are startled (low road) turn round and evaluate the situation
(high road); if it is a domestic cat you begin to relax, but if it is a menacing stranger you
remain alert.
Evidence in favour of Le Doux’s model comes from the study of the orbitofrontal cortex –
that part of the cortex that lies just above the eye orbits. The orbitofrontal cortex receives
information from the cortex itself and a variety of sensory systems (including taste, odour,
and visual signals). Significantly, the orbitofrontal cortex is in communication with the limbic
system including the amygdalae. In addition, it has been found that some neurons in the
primate orbitofrontal cortex respond to the sight of faces (Rolls, 1996). This link, therefore,
between the orbitofrontal cortex and the amygdalae provides just one example of how high
level cortical processes (events in the orbitofrontal cortext) may be involved in the emotional
response. This is evidence for the “high road” postulated by Le Doux (see Figure 10.5)
Figure 10.5 Pathways of fear. The amygdala receives information in two ways. The fast
route “takes no chances”: the fear reaction is alerted at the first sign of danger. The slow and
considered route is the product of cognitive processing of the fearful stimuli by higher centres
of the brain. This signal can then override the fast route if the danger sign turns out to be a
false alarm (for example, that snake was really a coiled up piece of rope). The hippocampus
supplies information about how the local circumstances have related to previous fearful
encounters – hence we may be afraid when we revisit the site of a very unpleasant experience
even if the experience is not repeated (for example, a scene of a mugging). USE EXISITNG
8.9
Cartwright, Evolution and Human Behaviour, Palgrave 2016
Sensory thalamus
Sensory cortex (auditory)
Hippocampus
Quick and dirty
low road
Sensory signal
(e.g. a noise)
Slow and
considered high
road
Memory and
information about
context
Sensory signal (for example, a noise)
Lateral nucleus
Amygdala
Emotional
response
Sensory thalamus ..part of the thalamus. A large mass of grey matter situated deep in the
forebrain. It relays to the cerebral cortex information received from a variety of brain
regions. A type of final filter for information going to cortex.
Sensory Cortex.. part of the cortex associated with processing sensory information
Lateral Nucleus ..one of several divisions in the amygdala. The lateral nucleus receives
information from the outside world via the sensory thalamus
Cartwright, Evolution and Human Behaviour, Palgrave 2016
Hippocampus… a brain structure containing a storage of explicit memories. The
hippocampus is involved with conditioned fear reactions. It stores information about
previous disturbing events and their contexts
10.3.4 Mirror neurons and the understanding of emotions
In Chapter 6 we noted how the recent discovery of mirror neurons suggests a means by which
individuals can understand the actions of others. Vittorio Gallese and colleagues (2004) have
advanced the hypothesis that emotions may also be recognised and understood by a mirror
neuron system. A crucial area of the brain where some evidence for this has been observed is
the insula.
The insula (also known as the lobus insularis or Island of Reil) lies within the cerebral cortex.
It is covered by parts of the frontal, temporal and parietal lobes. The anatomy of the insula
reveals two functional subdivisions: towards the front (anterior) lies a “visceral” sector, and
towards the rear a multimodal sector. The anterior sector receives connections from olfactory
and gustatory centres; it is also connected to the amygdala. The posterior portion receives
connections from the thalamus that convey interoceptive signals (that is, signals originating
within the body) such as emotional and homeostatic information. Damsio has proposed that
the insula, like the amygdala, is involved in mapping and processing visceral information
giving rise to the conscious experience of an emotion (Damsio, 2000).
Brain imaging studies have shown that the anterior insula is activated by sight of the facial
expression of disgust in others. Over 60 years ago Penfield and Faulk (1955) found that
direct electrical stimulation of the anterior insula of patients undergoing neurosurgery
brought about reported feelings of nausea and sickness (Penfield and Faulk, 1955). More
recently, Mary Phillips et al (1997) used fMRI imaging to investigate the response of the
amygdala and insula to fear and disgust respectively. The group found that the anterior insula
was activated when an observer witnessed the emotion of disgust on another face, and the
more disgust expressed on the observed face the higher the response. Wicket et al (2003) also
used fMRI to examine the activation of the brains of subjects both exposed to disgusting
odours and viewing a film showing others experiencing the emotion of disgust. The
experience of pleasing odours was used as a control. Interestingly, the same regions of the
anterior insula were activated by both the sight of the emotion of disgust on the faces of
others and the personal experience of disgust following the exposure to the unpleasant odour
(hence the appropriate title of Wicker at al’s paper: “Both of us disgusted in my insula …”).
Cartwright, Evolution and Human Behaviour, Palgrave 2016
All this provides evidence for the existence of structures in the brain that are active during the
first- and third-person experience of emotions. Such structures may form the substrate that
allows humans to empathise with others, and so could form a platform for a broader range of
interpersonal relations and social cognition itself.
References
Bard, K. A. (2005). Emotions in chimpanzee infants: the value of a comparative
developmental approach to understand the evolutionary bases of emotion. Emotional
development: Recent Research Advances. J. Nadd and D. Muir. Oxford, Oxford University
Press.
Damasio (2000). The feeling of what happens. London, Vintage.
Darwin, C. (1872). "The expression ofthe emotions in man andanimals." New York: D.
Appleton.
Gallese, V., K. C. and G. Rizzolatti (2004). "A unifying view of the basis of social
cognition." Trends in Cognitive Sciences 8(9): 396-403.
LeDoux, J. (1997). The Emotional Brain:the mysterious underpinnings of emotional life.
New York, Simon and Schuster.
McGaugh, J. L., B. Roozendaal and L. Cahill (1999). Modulation of memory storage by
stress hormones and the amygdaloid complex. Cognitive Neuroscience, 2nd edition. M.
Gazzaniga. Cambridge, MA, MIT Press.
Penfield, W. and M. E. Faulk (1955). "The insula: further observations on its function." Brain
78: 445-470.
Phillips, M. L., A. W. Young, C. Senior, M. Brammer, C. Andrew, A. J. Calder, E. T.
Bullmore, D. I. Perrett, D. Rowland, S. C. R. Williams, J. A. Gray and A. S. David (1997). "
A specific neural substrate for perceiving facial expressions of disgust." Nature 389: 495-498.
Rolls, E. T. (1996). "The orbitofrontal cortex." Philosophical Transactions of the Royal
Society B 351: 1433-1444.
Schiff, B. B. and M. Lamon (1994). "Inducing emotion by unilateral contraction of face
muscles." Cortex 30: 247-254.
Spence, S., D. Shapiro and E. Zaidel (1996). "The role of the right hemisphere in the
physiological and cognitive processing of emotional stimuli." Psychophysiology 33: 112-122.
Springer, S. P. and G. Deutch (1998). Left brain, Right Brain: Perspectives from Cognitive
Neurosciences. New York, Freeman and Co.
Thompson, R. F. (2000). The Brain. New York, Worth.
Weiskrantz (1956). "Behavioural changes associated with ablation of the amygdaloia
complex in monkeys." Journal of comparative and physiological psychology 49: 381-391.
Wicker, B., C. Keysers, J. Plailly, J.-P. Royet, V. Gallese and G. Rizzolatti (2003). "Both of
Us Disgusted in My Insula - The Common Neural Basis of Seeing and Feeling Disgust."
Neuron 40(3): 655-664.
Workman, L., S. Peters and S. Taylor (2000). "Lateralisation of perceptual processing of proand anti- social emotions displayed in chimeric faces." Laterality 5: 237-249.