W10 L16 Mem II Flashcards
Neural Correlates of Reinforcement
Dopamine plays an important role in reinforcement.
Axons of dopaminergic cells project to areas of the brain through three major pathways:
Nigrostriatal pathway connects substantia nigra with the striatum: involved in movement.
Mesocortical pathway connects the ventral tegmental area (VTA) to the cerebral cortex: involved in cognition, motivation and emotion.
Mesolimbic pathway connects the VTA to the nucleus accumbens (reward centre) . involved in reward and desire.
Instrumental Learning and the Basal Ganglia
▪ Complex behaviours (e.g. learning to drive a car with manual transmission) involves learning a set of rules.
▪ At first, complex behaviour can be slow and awkward to learn but with practice we become skilled; the learned behaviour becomes routine and automatic.
▪ When learned behaviours become automatic, they get transferred to the basal ganglia.
▪ Complex, automatic behaviours are instrumental in nature: we tend to make responses that are reinforcing.
Location of VTA and Nucleus Accumbens in the Rat
The bundle of axons that carry the information from the VTA to the nucleus accumbens (or VENTRAL STRIATUM) is called
the medial forebrain bundle (MFB).
Also vs is known as reward centre.
Dopamine Release in the Nucleus Accumbens, for animals treated using micro dialysis
▪ Electrical stimulation of the MFB or the VTA or administration of cocaine or amphetamine causes dopamine release in the nucleus accumbens.
▪ Natural reinforcers such as water and food also stimulates the release of dopamine in the nucleus accumbens.
Nucleus Accumbens Activity During Reinforcement, for humans using pet
▪ In humans, nucleus accumbens activity increases when people are presented with stimuli associated with money.
▪ Nucleus accumbens activity increases when heterosexual men press a lever that presented pictures of beautiful women (not handsome men).
Sensitive to pleasure and something we like, is na/vs/rc
Detecting Reinforcement Stimuli is not a given, as?
▪ A stimulus that serves as a reinforcer on one occasion may fail to do so on another.
▪ Dopamine neurons of the VTA are activated by stimuli that predict the occurrence of reward (Mirenowicz and Schultz, 1994; 1996).
- Monkeys trained to respond to an auditory stimulus to get a reward of fruit juice (reinforcing stimulus).
- During training, dopamine neurons of VTA showed a high rate of responding every time juice was delivered.
- Eventually, the VTA neurons only responded when the auditory stimulus was presented, not when the reward was delivered.
▪ VTA neurons signal something that has to be learned. If the rewarding outcome is expected, then there is nothing to be learned.
Prefrontal influence on VTA
▪ The prefrontal cortex provides an important input to the VTA.
▪ The neurons connecting these regions secrete glutamate which causes dopamine neurons in VTA to fire in clusters of action potentials (bursting or burst firing).
▪ Burst firing of VTA greatly increases the amount of dopamine secreted in the nucleus accumbens.***
▪ The prefrontal cortex is involved in complex executive functions which are goal directed.
▪ Presumably the prefrontal cortex activates a reinforcement mechanism when it detects that the animals behaviour is progressing towards its goal.
▪ The prefrontal cortex is also a target of dopamine neurons as well a source of their control. Reciprocal relationship!
Dynamic interaction, self firing like
Anterograde amnesia refers to the inability to learn new information or retain new information ‘after’ brain injury. Memory for events that occurred before the injury remain intact.
▪ Retrograde amnesia refers to the inability to remember events that occurred ‘before‘ the brain injury.
▪ Pure anterograde amnesia is
Rare, but most common (anterograde)
What did patient hm demonstrate?
H.M. received a bilateral medial temporal lobectomy to treat his seizures. He was 27 years of age.
▪ The surgery removed two thirds of his hippocampus and his entorhinal cortex.
▪ The surgery treated the seizures but left H.M. with serious anterograde amnesia.
However, H.M. was NOT impaired in all types of learning
Priming is when pre-exposure to a stimulus facilitates subsequent learning or memory.
H.M.’s performance improved significantly when tested later because he remembered the previous experience of seeing the picture
Intact Associative and Motor Learning Capabilities
▪ H.M. could acquire a classically conditioned eye blink response and showed retention of the task two years later.
▪ H.M. was successfully trained on an instrumental conditioning task in which he had to make a response to get money (his reward).
▪ H.M. was also successfully trained on the mirror-drawing test (a test of motor learning) in which he was required to draw a third outline in between a double outline of a star while looking only at his reflection in a mirror.
▪ Although difficult at first, H.M. improved with practice.
Declarative and Nondeclarative Memories
▪ Although amnesic patients show sparing of certain forms of learning, they do not remember anything about what they have learned.
▪ There are two major categories of memories:
Anterograde amnesics can acquire what type of memories?
nondeclarative memories
▪ Patient E.P. had viral encephalitis that destroyed much of his medial temporal lobe.
▪ Bayley and Squire (2002) presented patient E.P. with three word sentences. After learning, E.P. was tested by presenting him with incomplete sentences.
- VENOM causes FEVER (12 weeks to learn)
- VENOM causes ? (E.P. answered fever)
- VENOM induces ? (E.P. could not answer)
▪ E.P. was learning the words through associative stimulus- response learning.
Like press circle for pennies
The Anatomy of Anterograde Amnesia
▪ Damage to the hippocampal formation or regions that supply its inputs and outputs causes anterograde amnesia.
▪ The most important input to the hippocampal formation is the entorhinal cortex which in turn receives direct input from amygdala and the perirhinal cortex, and indirect input from all the association areas in the cortex.
▪ The perirhinal cortex receives information from the ventral stream, and the parahippocampal region receives information from the dorsal stream.
▪ The main outputs of the hippocampal formation come from the CA1 field and the subiculum which are often relayed back to the entorhinal cortex to the same regions that provide input.
Anoxia Damages CA1 Field of the Hippocampus
▪ During a brief coronary attack, patient R.B.’s brain was temporally deprived of oxygen due to a halt in blood flow (Zola-Morgan et al., 1986).
▪ The ensuing brain damage led to permanent anterograde amnesia. Five years after R.B.’s cardiac failure, he died and his brain was histologically examined.
▪ In R.B.’s brain, the CA1 field had completely degenerated.
▪ In monkeys and rats, a period of anoxia causing damage to the CA1 region causes severe anterograde amnesilotw of nmda receptors stimulated by glutamate, created extensive entrance of calcium.
Episodic memories (autobiographical memories) are those which we personally experience at a specific time and place; the event and the whole context. ▪ Semantic memory involves facts; knowledge of the world. We can access it quickly and effortlessly. They are independent of the context in which they were learned. ▪ Episodic and Semantic memory are types of
declarative memory
Hippocampal damage affects episodic memory
▪ Some patients who acquire hippocampal damage early in life show anterograde amnesia for episodic information but have intact semantic memories (Vargha-Khadem et al., 1997).
- Hippocampal damage alone is sufficient for episodic memory because of its reliance on context.
- Destruction of the hippocampus and the limbic cortex of the temporal lobe is necessary to prevent the consolidation of all types of declarative memory.
▪ Some patients with damage limited to the hippocampus acquired in adulthood, show both episodic and semantic memory impairments (Manns et al., 2003).
- Compensatory brain mechanisms mask observed deficits in adulthood; thus both, episodic and semantic memory require participation of the hippocampus.
Semantic Dementia
▪ Semantic dementia (Warrington, 1975) is a progressive neurodegenerative disorder characterised by a loss of semantic memory which is due to degeneration of the anterior temporal pole.
Part of frontal temporal pole dementias.
Significant.
▪ Semantic dementia patients often present with word-finding difficulties, aphasia, incomprehension of word meanings and visual agnosia (inability to match semantically-related pictures or objects).
