Brain and Behaviour Flashcards
What do emotions arise in response to?
changes in our surroundings that could have important consequences. These may be immediate (e.g., being confronted by a mug-
ger) or delayed (e.g., anticipating an examination). Some emotions are short-lived (surprise, humor) and these often arise when there is a discrepancy between what is expected and what actually happens, others are long-lived (e.g., jealousy, hatred).
What do emotions arise in response to?
changes in our surroundings that could have important consequences. These may be immediate (e.g., being confronted by a mug-
ger) or delayed (e.g., anticipating an examination). Some emotions are short-lived (surprise, humor) and these often arise when there is a discrepancy between what is expected and what actually happens, others are long-lived (e.g., jealousy, hatred).
Are emotional responses hard-wired or learnt?
some are hard wired—executed by neural circuits that are genetically specified during development—such as the universal aversive reaction of infants to bitter-tasting (potentially toxic) foods, but most (e.g., love) are probably learnt. Apparently hard-wired
responses need not be forever fixed; most adults come to like the bitter foods their culture teaches them is safe
What are the three components to an emotional state?
● A conscious cognitive component
● Visceral sensations arising from autonomic and endocrine events (e.g., feeling a rise in heart rate)
● Motor actions (e.g., characteristic facial expressions)
What makes the visceral sensations and cognitive aspects of the emotional state self-reinforcing?
There are learned associations between them.Realization of just how bad or good a situation is drives visceral changes, while conscious efforts to stem visceral sensation (e.g., controlled breathing) lessens emotional intensity.
How do emotions enhance survival?
- They are arousing and direct attention to important aspects of a situation so that it can be assessed as threatening or beneficial.
- Emotions are goads to useful action. We usually avoid snakes.
- The motor component (e.g., laughing or crying) communicates our emotional state to others, altering their behavior. Before it acquires language an infant can only
communicate its needs and desires by expressing its emotions. But also in adults
emotions act as a powerful form of nonverbal communication. This is crucial for social interactions.
What is an affect?
The subjective experience of emotion, especially that leading to action, is termed affect.
The core of the limbic system consists of the affective striato-thalamo-cortical circuit and its connections with the amygdala what is the set up of this loop?
laid out in much the same
pattern as the motor loop, except that the striatal component is the ventral striatum (nucleus accumbens, nAc) which projects to the ventral pallidum (ventral part of the
globus pallidus). The ventral pallidum relays via the mediodorsal thalamus to the anterior cingulate cortex and medial orbital prefrontal cortex. The loop is closed by connections from the cortex back to the nucleus accumbens. The affective loop has reciprocal connections with the amygdala
What is the amygdala responsible for?
responsible for fear learning, and is modulated by the dopaminergic mesolimbic system which is concerned with reward learning.
Output of the nucleus accumbens goes to the compact part of the substantia nigra. What does this allow?
the activity of the motor and cognitive striato-thalamo-cortical circuits to be modified, providing for some of the motor and the cognitive aspects of emotional states.
What is the affective motor pathway?
Output of the amygdala goes to the hypothalamus and a variety of brainstem structures that organize motor, arousal, and visceral aspects of emotions. Facial expressions engendered by emotions—smiling, crying, and so forth—are brought about by extrapyramidal
motor pathways that run in the brainstem reticular formation.
What is a duchenne smile?
Patients with unilateral
damage to corticobulbar fibers descending from the motor cortex have voluntary motor paresis on the opposite side. When asked to smile on demand their smile is lopsided. However, when genuinely amused their smile is natural and bilateral (Duchenne smile) because different emotion-driven motor pathways are engaged.
What is the Papez circuit?
The anterior cingulate cortex projects to the entorhinal cortex that acts as a gateway for all neocortical input to the hippocampus. Efferents leave the hippocampus by way of the fornix for the hypothalamus. Output from the mammillary bodies (by way of the mammillothalamic tract) goes via the anterior thalamic nuclei back to the anterior cingulate cortex. The hypothalamus also has connections with the prefrontal cortex.
What is the role of the Papez circuit?
mediating explicit learning (learning that can be consciously recalled) during emotional states
What is the amygdala?
a cluster of nuclei in the white matter of the temporal lobe.
Where does sensory information enter the amygdala?
Olfactory input runs from the olfactory bulb to the corticomedial nucleus. Sensory information from other modalities (vision, hearing, somatosensory) enters the basolateral nuclei
from specific thalamic nuclei and their corresponding areas of sensory cortex.
Other than sensory information, what other input does the basolateral nuclei receive?
● The state of the viscera from the hypothalamus
● Arousal status from the locus coeruleus and nucleus basalis of Meynert
● Cognitive processing by the orbital prefrontal cortex
What is the output from the amygdala?
It amygdala is from its central nucleus and follows two anatomical pathways. Efferents to the hypothalamus, septum, and several brainstem nuclei go via the stria terminalis, while the ventral amygdalofugal pathway conveys connections to the nucleus accumbens.
How does the amygdala drive fear responses?
It has access to species-specific hard-wired neural representations of scary things
How does fear conditioning occur?
occurs when a neutral stimulus (CS), such as a tone, is paired with a noxious stimulus (US), such as a brief electric foot shock. After several tone–shock pairings the tone becomes a negative reinforcer and it elicits conditioned fear responses (CR), including autonomic, endocrine, and behavioral
signs of fear.
How has the role of amygdala in fear learning been documented?
● The connections of the amygdala supports its role in aversive learning because it activates the cholinergic attentional system, the sympathetic nervous system, and the release of stress hormones
● Firing of amygdala (central nucleus) neurons correlates with the development of the
fear responses.
● Lesions of the amygdala prevent acquisition of new conditioned fear responses or expression of preexisting ones, although they do not affect autonomic responses to aversive stimuli (e.g., the defense reaction) which are organized by the hypothalamus
● Electrical stimulation of the amygdala in humans during surgery evokes feelings of
apprehension and fear.
● Brain scans show increased activity in the amygdala in humans shown fearful faces.
This response is impaired in people in whom the amygdala is calcified, even though they are still able to identify individual faces. Hence the neural system for emotional memory is distinct from that for explicit memory of faces.
When does evaluation of a stimulus by the amygdala occur?
It begins earlier than any conscious cognitive appraisal of the situation.
Amygdala fear learning is implicit learning; what does this mean?
the fear responses cannot be consciously generated. The amygdala develops more rapidly during infancy than the hippocampus (responsible for explicit memory). During this time fearful memories may be acquired which cannot later be consciously accounted for. This could underlie specific phobias.
Where are long-term emotional memories stored?
in the cerebral cortex rather than the amygdala: presentation of fear-evoking stimuli activates visual association cortex and orbital prefrontal cortex as well as the amygdala.
What does fear learning of the amygdala involve at a cellular level?
Involves NMDA receptor-dependent long-term potentiation similar to that underlying hippocampal learning.
What allows cognition to influence emotional states and vice versa?
Extensive interconnections between different parts of association neocortex. Lesions of the orbital prefrontal cortex reduce emotional responses (e.g., aggression) in primates, while in humans lesions of the anterior cingulate cortex reduce the emotional distress of chronic intractable pain.
What is motivated/ goal- directed behavior?
Behavior that is driven by internal states or external events and which is aimed at achieving a particular outcome. Some motivated behavior occurs in order to satisfy physiological needs. Goal-directed behaviors like this are homeostatic and normally self-limiting as the internal state is switched off (sated) by consumption. Much motivated behavior is not so straightforward because it occurs in the absence of any obvious physiological deficit.
What is a positive reinforcer?
Any stimulus that increases the probability of a motivated response occurring. An animal will work to get access to a positive reinforcer.
What is aversive behavior?
a reinforcer is said to be negative if the animal works to avoid the stimulus, in which case it is displaying aversive behavior.
The reinforcing quality of a stimulus depends on context. How is food an example of this?
food is a powerful reward to a hungry person but its positive reinforcing quality diminishes with satiety. However, a particular food may still be a positive rein- forcer if it is novel and sufficiently delicious even if the person is not hungry. Hence the motivation to eat is a complex interplay of internal state, external cues, and memory.
What are the two pathways that dopaminergic neurons ascend from the ventral tegmental area (VTA) as?
They ascend to the nucleus accumbens (nAc, ventral striatum) as the mesolimbic system and to the frontal cortex (including the cingulate and orbitofrontal cortex) as the mesocortical system
Why is the Mesolimbic system described as the reward system?
●Firing of mesolimbic neurons increases in the presence of natural reinforcers such as food.
●Conscious, behaving rats will forego food or sex in order to stimulate their own mesolimbic neurons by pressing a lever to deliver a small current through electrodes chronically implanted into the medial forebrain bundle; a technique termed intracranial self-stimulation (ICSS)
●Natural rewards, ICSS, and addictive drugs all increase the release of dopamine from mesolimbic terminals in the nucleus accumbens, and the reinforcing properties of all three are blocked by dopamine D1 receptor antagonists.
How do learned associations with a reward occur?
VTA neurons fire in response to a natural reward and the dopamine release facilitates
learned associations with the reward, in animal studies a conditional stimulus with which the reward has been paired. The learning occurs via the nucleus accumbens and the affective basal ganglia circuit. Subsequent firing of the VTA neurons depends on the predictability of the reward. Unexpected or novel rewards elicit a strong response, although this declines with repeated presentation. Predicted rewards have little effect, though conditioned stimuli associated with them continue to elicit dopamine release.
What happens with Omission of a predicted
reward?
reduces mesolimbic activity. The immediate response to omission of an expected
reward is to persevere with the activity that usually provides it. So, low activity of mesolimbic neurons when a predicted reward is missed promotes reward-seeking behavior.
What is the major target of the mesolimbic system?
The nucleus accumbens. Has GABAergic medium spiny neurons.
What is the output of the nucleus accumbens?
project to the GABAergic cells of the ventral pallidum (VP). Phasic dopamine release from terminals of VTA cells excites the MSNs, particularly if this coincides with excitatory input from the cortex or amygdala. Activity of the MSNs inhibits the GABAergic VP cells, hence disinhibiting the affective basal ganglia circuit. Distinct ensembles of MSNs respond differentially to cues associated with specific rewards.
What is the role of the cingulate and orbitofrontal cortices in reward pathways?
respond to rewards and associated stimuli in a manner that depends on their predictability and seems to be concerned with evaluating their overall salience (importance) and determining the intensity of the behavioral response. In some cases at least the prefrontal cortex initiates goal-directed behavior via glutamatergic connections to the nucleus accumbens.
How are the positive reinforcing properties of a drug assessed?
by self-stimulation studies which measure the extent to which animals (usually rats or monkeys) will work to get a dose of the drug.
What are conditioned place preference studies?
reveal that the context in which drugs are taken is important. Animals are first exposed to one environment when drugged and to a different environment when non-drugged. Next, the animals are given a choice
between the two environments (they can now move freely between them) and the time spent in each is recorded. With positively reinforcing drugs, animals spend more time in the environment they experienced in the drugged state. This is context-dependent learning and shows that learning is important in addictive behavior.
What is the concept of tolerance?
On repeated administration a drug becomes progressively less effective, so the dose has to be increased if the original action is to be maintained. The precise mechanism for tolerance depends on the drug, but includes enzyme induction, changes in receptor numbers, and alterations to second messengers. Tolerance does
not necessarily lead to addiction
What is dependence?
This occurs when biological changes brought about by the drug are such that normal functioning is only possible when the drug is present.
What is abstinence/ withdrawal syndrome?
If a drug is withheld after dependence is estab-
lished an abstinence syndrome results which is extremely unpleasant and lasts until the long-term biological changes that brought about dependence have abated. Hence, addiction (the need to take the drug repeatedly) can be driven as much by the aver-
sion to withdrawal as by the positive reinforcing qualities of the drug. In rare cases with some drugs (e.g., alcohol) withdrawal can be fatal.
What is craving?
The intense longing for a drug felt by addicts is a learned response that long outlasts the abstinence syndrome. Addicts form memories which associate the pleasure produced by the drug with the environment and cues that accompany the drug taking. Subsequent exposure to the same context causes craving.
What feature of craving corresponds with the much more intense motivation of addicts to seek the drug than natural rewards?
Brain imaging shows that cocaine-addicted subjects have increased activity in the cingulate and orbitofrontal cortices in response to stimuli associated with cocaine availability but decreased activity when presented with stimuli associated with natural rewards, compared to
non-addicts.
How does the effect of addictive drugs on the brain reward system differ from that of natural rewards?
unlike natural rewards, which when familiar cease to elicit dopamine release, addictive drugs continue to cause dopamine release with repeated exposure, resulting in dysregulation of the reward and affective basal ganglia circuits, and eventually long-term neuroplasticity that underpins craving and compulsive drug-seeking behavior.
How does cocaine produce tolerance?
by blocking the dopamine transporter (DAT) in the presynaptic terminals of mesolimbic neurons, limiting dopamine reuptake, so the concentration of transmitter in the synaptic cleft is raised. This causes downregulation of postsynaptic dopamine receptors. In addition dopamine binding to presynaptic receptors reduces dopamine synthesis and release. The overall effect is that higher amounts of transmitter, and hence drug, are needed to achieve the same level of dopamine transmission. When drug use stops, dopamine transmission in the mesolimbic system drops below normal.
how does creb overexpression contribute to abstinence syndrome?
Activation of D1receptors, which are positively coupled to cAMP, switches on transcription of the creb gene. CREB (cAMP response element binding protein) is itself a transcription factor that influences the expression of genes with the cAMP response elements (cre) in their regulatory domains; that is, genes switched on by increases in cAMP. When the drug is withheld, the CREB changes reverse with a time course that matches the abstinence syndrome
What is the neurobiology behind transition from acute drug responses to chronic plastic changes in addiction?
due to a gradual increase in the expression of a Fos family transcription factor, DFosB, in the nucleus accumbens. This molecule increases the expression of GluR2 AMPA receptors, cell signaling molecules, and brain-derived neurotrophic factor (BDNF), which can stimulate dendritic growth. the mesolimbic system
becomes more sensitive to the effects of the drug, overwriting the preexisting tolerance.
How does the origin of craving differ in the early and later stages of addiction?
In the early stages of drug use craving arises from the release of dopamine in the nucleus accumbens. As addiction takes hold and dopamine transmission in the mesolimbic system reduces, increased metabolic activity in the orbitofrontal cortex contributes to craving. This transition is due to glutamate-mediated plastic changes in ventral tegmental area, nucleus accumbens, and cortex akin to that which underpins learning in the hippocampus and elsewhere, namely long-term potentiation (LTP) and long-term depression
How does a recent history of drug experience alter the direction of direction of plasticity at nAc excitatory synapses?
LTP occurs in the medium spiny neurons during a drug-free period after cocaine addiction has been established. This is accompanied by increased numbers of AMPA receptors and dendritic spines on MSN cells, making them more sensitive to excitatory inputs from the orbitofrontal and cingulate cortex, and amygdala, some of which encode drug-contextual learning. Remarkably, just a single dose of cocaine reverses this to bring about LTD, a reduced responsiveness to glutamate, most probably by NMDA
receptor-controlled endocytosis of AMPA receptors.
How does inhibition of nucleus accumbens MSNs (GABAergic projection neurons), for example by
LTD, promote reward-seeking behavior?
inhibition of nucleus accumbens MSNs (GABAergic projection neurons), for example by LTD, promotes reward-seeking behavior,
What does reinstatement of drug-seeking now depend on?
depends on dopamine release not in the nucleus accumbens but in the amygdala and prefrontal cortex, probably due to plastic changes there.
Eating is a goal-directed behavior, what is it controlled by?
controlled in the shorter term by hunger signals, which motivate feeding, and satiety signals, which reduce it.
What two types of agents affect appetite?
An agent, neuron or pathway which stimulates appetite is said to be orexigenic, those which suppress appetite are anorexigenic.
