University Studies 15A:
Consciousness I
Emotion
Emotion will be a central element in our
account of the neuroscience of consciousness.
The systems that underlie what we think of as emotion provide a way to
account for saliency, what grabs our attention.
But it goes much deeper.
It lies at the heart of our manner of engaging the world.
It structures the subjective quality of what it is like to be in the world.
“Emotion” as we shall discuss it, has three distinct aspects:
1. We will begin with a substratum of “background feelings” deriving from the
brain stem.
2. We next will consider “primary emotions,” the hardware interrupts of the
cognitive system.
3. We then will begin to look at how processes of learning elaborate primary
emotions into the core of the semantic system and simultaneously
incorporate the background feelings into the subjective dimension of the
semantic network
Part One: the Base Beat from the Brain Stem
Our story begins with a sad but rare affliction, hydranencephaly.
Sometimes the Telencephalon of a fetus suffers
injury and never develops into the cortex, and an
infant is born with just the brain stem and
diencephalon.
However, this fact usually is not discovered until several weeks after birth.
During the first weeks after birth, the infant’s cortex does not have sufficient
myelin to function significantly, and the body relies primarily on the brain
stem and diencephalon structures to function.
As Antonio Damasio describes them, “To a limited but by no means negligible
extent, they can communicate with their caregivers and interact with the
world…. [T]hey move their heads and eyes freely, they have expressions of
emotions on their faces, they can smile at a stimulus that one would expect a
normal child to smile at—a toy, a certain sound—and they can even laugh and
express normal joy when they are tickled.” (Self Comes to Mind, pp. 80-81)
That is, the brain stem, aided by the thalamus and colliculi, has an astonishing
amount of processing power.
For humans this design is necessary because the cortex simply is not function
for the first few weeks after birth as its basic networks are being prepared and
trained.
The brain stem tracks most of the visceral information provided to the brain:
Heart rate
Oxygen levels
Perspiration and blushing
Pain (both mechanical and thermal)
The state of contraction of the smooth muscles of the gut, arteries, and
lungs
Collectively, the transmission of this information to the brain is called
interoception.
It turns out that the brain stem passes all this sensory data on to the thalamus.
The thalamus in turn passes it to a fifth lobe.
We know four lobes at present:
1. Occipital lobe
2. Parietal lobe
3. Temporal lobe
4. Frontal lobe
The Insula
Meet the fifth:
Although the insula is a complex set of regions, at least part of it appears to
serve as the cortical equivalent of the primary visual cortex for visceral data.
For example, there appears to be a body
(somatotopic) map for different types of pain
The insula also processes and organizes the other
forms of data.
It then passes this processed data upstream to
the amygdala, hippocampus, and multimodal
integration areas.
That is, via the insula, the brain integrates
visceral responses into its systems for
memory, decision, and saliency.
Our heartbeat (and perspiration) on our first
dates are part of episodic memory courtesy
the insula and its ties to the brainstem.
Damasio compellingly argues that the brainstem and the insula provide the
“feel” of experience as it is represented in the cortex.
This system provides a core “self,” a representation of the visceral subject in
the cortex that then becomes elaborated through its integration and
articulation within the systems for memory and meaning.
This “self” system functions all the time, providing a steady stream of
information about the visceral body to the cortical regions responsible
for assessment of the current state of the world.
The cortical system for assessing the incoming streams of data when at
rest and without attentional focus is the “Default Mode” network. (We
will discuss the network next week.)
Part Two: Emotion
“Affective neuroscience,” the neuroscientific study of emotion, sees
primary “emotions” as a set of interfaces (i.e. specialized brain structures)
that tells the cortex to pay attention to immediate needs.
Baars and Gage list seven basic physiological “emotion” systems:
1. FEAR (fear, anxiety)
2. SEEKING (interest, curiosity)
3. RAGE (anger, contempt)
4. PANIC (sadness, shyness, guilt shame)
5. LUST (erotic feelings, jealosy)
6. CARE (love)
7. PLAY (joy, happiness)
It is important to get the argument here right.
The basic idea is a distinction between deep, primitive triggers and highly
articulated emergent behavior.
Consider two examples.
The PANIC system is perhaps built upon a very simple “cyclical distress”
mode.
New-born infants experience periods of cortisol-mediated distress that
appears to be unrelated to any particular external cause.
This distress often can be extinguished simply when a face appears in the
visual field or if the infant is picked up.
How the infant analyzes the elements associated with this distress and with
relief from the distress will lay the foundation for a wide class of social
emotions.
The SEEKING system may be built on a dopamine-mediated positive response
to the unexpected.
For a new-born infant, almost everything is unexpected.
As the infant becomes just a bit older and both sensory cortices and memory
systems become functional, how different categories of the unexpected
turn out and under what circumstances will shape patterns of engagement
with the world.
All of this begins to happen long before the infant has language and before
any later episodic memories are made.
These early encounters between the primary emotional systems and the
world of just barely processed objects will lay the foundation for the “self”
and the semantic network of which the “self” is a part.
Note the role of the insula in these emotions (the viscera make their contribution):
Many years pass and we get a highly articulated world of emotional
categories:
However, affective neuroscience is mostly concerned with the early story and
with the on-going systemic relations between the “primary emotion”
systems and the cortical regions that feed into and receive input from the
“primary emotions.”
I will follow Baars’ and Gage’s example and consider the two best studied
systems, FEAR and SEEKING.
The center of the FEAR system is
the amygdala, the subcortical
structure next to the end of the
hippocampus
amygdala
hippocampus
Although small, the amygdala is internally complex and has complex afferents
(pathways of signals coming in) and efferents (pathways for signals going out to
other regions.) Below is the flow of activation started by sensory data.
Baars and Gage present the pathways with a medial view of the brain:
Afferents
(Note that Baars and Gage do not show the connections to the sensory association areas here)
Efferents
(Note that Baars and Gage do not show the connections to the sensory association areas here)
The amygdala’s connections to the visual system
(Note the connections to both the visual object network (ITC) and to the primary visual cortex)
The result of all these connections are the two distinct paths to activation of the
amygdala: the so-called “low road” and the “high road”
The visual system also uses
the “low road:” the superior
colliculus receives input from
the thalamus. It will activate
the amygdala if there is a dark,
curved shape in the periphery
of vision.
Visual discrimination through
this route is very poor: this is
a “better safe than sorry”
design that has survived from
early ancestral primates.
Once the amygdala is activated, attentional resources and body-state resources
are turned to attend to the sensory data and the internal analysis.
The “feeling” of fear comes from the hormones let loose in the process:
Note that the hippocampus is a target both
for the Noradrenaline (“fight-or-flight”
response: increased heart rate, glucose
into blood stream) and the Cortisol (stress:
increase blood glucose). This will be
important in learning.
The central system for the SEEKING system are the Dopamine Pathways.
Note once again the pattern of two
pathways:
The first is subcortical: the
“mesolimbic dopamine pathway”
between the VTA in the brainstem
and the nucleus accumbens (part of
the basal ganglia) in the forebrain.
The second, cortical pathway builds
on the first: the “mesocortical
dopamine pathway” is between the
orbitofrontal cortex (right above the
“orbits” of the eyes) and the VTA.
For functional connectivity once the dopamine is produced, it operates in the
frontal cortex far beyond the orbitofrontal cortex that is part of the control
loop:
The result of the connection between the direct dopamine pathways and the
rest of the cortex is a system that responds to errors in prediction of rewards.
As Baars and Gage explain:
1. Dopamine neurons fire at unexpected rewards and novel events.
2. Dopamine neurons stop firing when rewards become predictable or the
event ceases to be novel.
3. Dopamine neurons start firing when conditioned stimuli (eg., a bell ringing)
prove to predict a reward (the food pellet arriving, an unconditioned
stimulus).
4. Dopamine neurons are inhibited when the conditioned stimulus fails to
produce the predicted reward.
5. Dopamine neurons stop firing when the conditioned stimulus reliably
predicts the reward.
Hence, the dopamine system fires at errors in prediction of rewards.
This does not seem very remarkable, but the brain really “likes” dopamine
and is built to pay attention to what produces dopamine.
In adults, dopamine is involved in addictions, cravings, an compulsive
behavior.
In babies, dopamine responses help shape what is noticed and remembered.
It helps shape the dimensional logic of memory and the structure of the
semantic system.
That is, the emergent self, our likes, dislikes, values, what we notice, and the
manner in which we engage the world all are fundamentally mediated by a
developmental logic shaped by the primary emotions.