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LECTURE 23: EMOTIONS, MOTIVATION, AND DRUGS OF ABUSE
REQUIRED READING: Kandel text, Chapters 50, 51
Emotion and Feeling are two interconnected states.
Emotion is a group of physiological and motor responses to a set of stimuli.
These emotional responses communicate our state to others, prepare us
or drive us for consequent action, and have powerful effects on our
unconscious (implicit) memory of the stimulus events.
Feeling represent the conscious (explicit) awareness of our emotional state.
EXAMPLES:
The taste of a great dessert can elicit the emotion of enjoyment and
satisfaction and the feeling of having something delicious
Upon hearing a joke, one may experience the emotion of laughter
and the feeling of a funny experience
EMOTIONS EXERT POWERFUL INFLUENCES ON MOTIVATIONAL BEHAVIOR
EMOTIONAL EXPERIENCES CAN BE STEREOTYPICAL OR SUBJECTIVE
Hearing an unanticipated loud explosion triggers a startle emotion
characterized by heightened awareness, shivering or freezing,
elevated pulse and blood pressure, and a specific facial expression,
while triggering the feeling of fear
Seeing David Ortiz of the Boston Red Sox hit a home run against
the New York Yankees can trigger exhaltation, sadness,
or nothing depending upon one’s interest in baseball and whether
one is a Red Sox or Yankees fan
Why?:
Just as conscious cortical activity can shape our reflexive responses
to stimuli, it can also shape our automatic
emotional responses to certain stimuli
Conscious decisions can shape value (ethical) judgments
which inform our emotional responses
THE LIMBIC SYSTEM CONTROLS GENERATION OF EMOTIONAL STATES
THE AMYGDALA IS CRITICAL FOR EMOTIONAL RESPONSES,
PARTICULARLY TO NEGATIVE EMOTIONS
LEARNED EMOTIONAL RESPONSES ARE PROCESSED IN THE AMYGDALA
AMYGDALA AND HIPPOCAMPUS ARE SEPARATELY NEEDED FOR THE FEARFUL
AND COGNITIVE COMPONENTS OF PAST EXPERIENCE
Individuals with brain lesions were shown different colored slides, and
some slide colors were followed by a loud startling noise
LESION
NONE
AMYGDALA
HIPPOCAMPUS
BOTH
CONSCIOUS MEMORY
OF COLORS
YES
LEARNED FEAR
OF COLORS
YES
YES
NO
NO
YES
NO
NO
DEAZOPENE (VALIUM) INHIBITS FEAR AND ANXIETY
Valium is a widely used medication used to reduce anxiety and fear,
often prescribed prior to surgeries without general anesthesia
Valium interacts with GABA ionotropic receptors, and enhances
GABA-induced chloride conductance. At optimal dosages,
valium inhibits firing of neurons in fear and anxiety circuits
Valium is often used, often addictively, as a means to
relieve “life” stress
MOTIVATIONAL BEHAVIORS ARE OFTEN DIRECTED TOWARDS
MAINTENANCE OF PHYSIOLOGICAL HOMEOSTASIS
The hypothalamus plays a pivotal role in homeostatic motivations,
acting as physiological sensor and coordinating autonomic
and motivational responses
Examples:
Thermal regulation: Certain hypothalamic neurons fire at different
rates at different temperatures. Deviation from set point
(37oC in humans) triggers other regions of hypothalamus
initiate autonomic functions and behavioral drives
Appetite: Hunger level is driven in part by hypothalamic control.
Certain hypothalamic neurons have receptors for a hormone,
leptin, which is produced by fat tissue. Leptin suppresses apetite.
SOME MOTIVATIONS ARE NOT DRIVEN BY DIRECT PHYSIOLOGICAL NEEDS,
BUT BY PLEASURABLE EMOTIONS AND ANTICIPATION OF PLEASURE
We (and rats) tend to eat more calories of flavorful food than
bland diet
Sexual behavior is drive towards pleasure fulfillment
Stimuli that are pleasurable are believed to signal “pleasure”
by activating certain midbrain dopaminergic neurons in
the ventral tegmental area (VTA) that project to the
nucleus accumbens (NA) region of the forebrain
Rats can be implanted with electrodes into the VTA, with
stimulation triggered by the animals pressing a lever.
Such animals learn to frequently self-”reward” by pressing the lever
MANY DRUGS OF ABUSE ACT BY PROMOTING THE
DOPAMINERGIC PLEASURE CIRCUIT
Cocaine and amphetamines act by blocking dopamine reuptake transporters,
resulting in prolonged dopaminergic signaling.
These drugs cause sensory-independent sensation of pleasure and
also enhance pleasure associated with certain stimuli
Nicotine mediates excess release of VTA dopamine by stimulating
presynaptic cholinergic receptors on VTA axons
Mu opiates (e.g., morphine) act by inhibiting GABAergic neurons that
project to VTA dopaminergic neurons
DRUG CRAVING CAN BE TRIGGERED BY SENSORY CUES ASSOCIATED
WITH DRUG USE: A FORM OF CONDITIONED STIMULUS
Drug exposure follows a sequence of behavioral and sensory cues
that act as conditioning stimuli to the drug unconditional stimulus
Consequence is conditioned response, whereby the cues alone trigger
anticipation of drug “reward”