Chapter 13 (pages 450-465)

CHAPTER 13 (pages 453- 465) Instrumental Conditioning Basal Ganglia 2 major path ways between the sensory association cortex and motor association cortex: direct transcortical connections & connections via the basal ganglia and thalamus. Transcortical connections: Involved in acquisition of episodic memories (complex perceptual memories of sequences of events that we witness or are described to us) Also involved in acquisition of complex behaviors that involve deliberation or instruction. As learned behaviors become automatic and routine, they are ?transferred? to the basal ganglia. As we deliberately perform a complex behavior, the basal ganglia receive info about the stimuli that are present and the responses we are making. As the behaviors are repeated again, and again, the basal ganglia begin to learn what to do. Eventually, they take over most of the details of the process, leaving the transcortical circuits free to do something else. Caudate nucleus and putamen: receives sensory info from all regions of the cerebral cortex. Also receives sensory info from the frontal lobes about movements that are planned or are actually in progress. The outputs of the caudate nucleus and putamen are sent to the globus pallidus (another part of the basal ganglia) The outputs of globus pallidus are sent to the frontal cortex: To the premotor and supplementary motor cortex -Where plans for movements are made To the primary motor cortex- where plans for movements are executed Lesions of the basal ganglia disrupt instrumental conditioning but do not affect other forms of learning. Reinforcement Maze learning in rats (Milner): Attempted to determine whether electrical stimulation of the reticular formation would facilitate maze learning in rats. They planned to turn on the simulator briefly each time the animal reached a choice point on the maze. Medial forebrain bundle (MFB): A bundle of axons that travel in a rostral-caudal axis from the midbrain to the rostral forebrain. Best and most reliable location for stimulation The activity of dopaminergic neurons play a big part in this phenomenon 3 major systems of dopaminergic neurons: nigrostriatial system, mesolimbic system, mesocortical system nigrostriatial system: involved in the control of movement. mesolimbic system: begins in the ventral tegmental area (VTA) of the midbrain and projects to the amygdala, hippocampus, and the nucleus accumbens (NAC). mesocortical system: begins in the VTA but projects to the prefrontal cortex, the limbic cortex and the hippocampus. Functions of the Reinforcement System: Must perform 2 functions => 1. Detect the presence of a reinforcing stimulus?2. Strengthen the connections between the neurons that detect the discriminative stimulus and the neurons that produce the instrumental response. Detecting Reinforcing Stimuli: Reinforcement occurs when neural circuits detect a reinforcing stimulus and cause activation of dopaminergic neurons in the VTA. The reinforcement system is not automatically activated when particular stimuli are present; its activation also depends on the state of the animal. The reinforcement system appears to be activated by unexpected reinforcing stimuli. The activity of dopaminergic neurons sends a signal that there is something to be learned; if the delivery of the reinforcer is already expected, then there is nothing to be learned. The prefrontal cortex provides an important input to the VTA. The terminal buttons of the axons connecting these two areas secrete glutamate (excitatory NT) The activity of these synapses make dopaminergic neurons in the VTA fire in a bursting pattern => greatly increases the amount of dopamine they secrete. The prefrontal cortex turns on the reinforcement mechanism when it determines that the ongoing behavior is bringing the organism nearer to its goal. Strengthening Neural Connections: Dopamine and Neural Plasticity: Instrumental conditioning involves 3 elements => Discriminative stimulus, a response, a reinforcing stimulus Considering a rat learning to press a lever to obtain food: discriminative stimulus ? (the sight of the lever) activates weak synapses on motor neurons which causes the rat press lever. the response ? activates strong synapses, making the neurons fire. Reinforcement mechanism triggers the secretion of a NT or neuromodulator throughout the region in which the synaptic changes take place The release of dopamine in a variety of brain locations affects learning, plays a critical role in long-lasting long-term potentiation. Long-term potentiation is essential for instrumental conditioning ?dopamine is an essential ingredient in long-lasting long-term potentiation. the presence of dopamine & the activation of NMDA receptors in the nucleus accumbens is necessary for instrumental conditioning to take place. Prefrontal cortex is a target of dopaminergic neurons as well as a source of their control. Dopamine facilitates LTP in the lateral amygdala Relational Learning Human Anterograde Amnesia ? Human anterograde amnesia: difficulty in learning new info. ability to remember events that occurred before the brain damage occurred?inability to retain info they encounter after the damage. can also be caused by damage to the temporal lobes. critical site of damage was the hippocampus Human retrograde amnesia: inability to remember events that happened before the brain damage occurred. Korsakoff?s Syndrome: Permanent anterograde amnesia usually caused by brain damage resulting from chronic alcoholism or malnutrition. confabulation: (another symptom of Korsakoff?s Syndrome)reporting of events that did not take place without the intention to deceive. can contain mixtures of events that really occurred or they can be completely imaginary. they appear to believe what they are saying really occurred. Explicit (declarative) and Implicit (nondeclarative) Memories: Explicit memory: memory that can be verbally expressed patients with anterograde amnesia are unable to talk about the experiences they?ve had since the damage. Implicit memory: includes instances of perception, stimulus-response, and motor learning that we are not necessarily conscious of. does not depend on the hippocampal formation do not require deliberate attempts on the part of the learner to memorize something. does not include facts/experiences; they control behaviors Anatomy of Anterograde Amnesia ? Damage to the hippocampus or to the regions of the brain that supply its inputs and receive its outputs cause anterograde amnesia. The most important input to the hippocampal formation is the entorhinal cortex neurons there terminate in the dentate gyrus, CA3 & CA1. receives inputs from the amygdala, various regions of the limbic cortex, association regions of the neocortex, either directly or via the perirhinal cortex and the parahippocampal cortex. Perirhinal cortex receives visual info from ventral stream parahippocampal cortex receives visual info from dorsal stream The outputs of the hippocampal system come primarily from field CA1 and the subiculum. The hippocampal formation also receives input from the subcortical regions via the fornix. The fornix connects the hippocampal formation with the mammilary bodies (located in the posterior hypothalamus) the cause of anterograde amnesia is degeneration of the mammillary bodies.