PSYC 371 - DLPFC

Wisconsin card sorting test

• 3 categories: same number, shape and color

• subjects learn which rule is correct and then flexibly adjust choices when rule changes

• DLPFC damage especially disrupts ability to change strategies and follow new rules

• DLPFC damage patients may be able to understand the new rule but they perseverate

• they also randomly abandon successful strategies

Rodent PFC needed to shift strategies in the plus maze

• rats trained in place version and then response version or vice versa

• inactivating frontal (prelimbic + infralimbic) cortex did not impair initial learning

• inactivation impaired rats’ ability to switch from one strategy to the other

• prelimbic and limbic cortices are rodent areas that perform the same executive functions that DLPFC performs in primates

DLPFC also contributes to working memory

• objective-selective PF neuron has high firing rate in “what” delay where the monkey had to remember what the sample object was

• ^^ firing when no movement is needed suggests that DLPFC neurons store info in working memory and not just involved in planning movement

• working memory could contribute to other functions in planning and behaviour like detection of rule changes in WCST

• location-sensitive pF neuron fire during “where” delay

• DLPFC lesions impair performance on delayed response tasks

Rodent PFC required for working memory in radial arm maze

• training phase: rats learn that 4/8 arms have food

• test: rats have to get food from the other 4 arms (win-shift or delayed non-match to place)

• inactivating PFC, hippocampus and hippocampus-PFC before testing increases errors

• hippocampus important when delays are longer than 30 mins

• PFC and hippocampus work tgt to know the environment and remember the location of rewards

radial arm maze method

• Lidocaine: blocks Na+ channels (reversible)

• Lidocaine bar has significantly greater amount of errors than saline vs. day before injection

Radial arm maze long term vs working memory

• long term memory: the rat needs to remember the rules of maze

• working memory: the rat needs to remember which arms it visited during training phase

• PFC is responsible for the continuous updating of information, distinct from the long-term learning of the maze layout

Radial arm maze errors

• within phase: the rat revisits the same arm in test phase twice

• across phase: the rat revisits the same arms in training phase and testing phase

Mechanism underlying working memory remains unknown

• persistant neural activity: neurons continuously fire during the “delay” period

  • Persistent Intrinsic Firing

  • Persistent reverberatory network activity

• synaptic plasticity

Persistent Intrinsic Firing

• ca 2+ influx and afterdepolarization (ADP) keeps a neuron active even after the stimulus is removed

• only works if the stimulus is present for long enough because short stimulus is not enough to trigger positive feedback loop of ADP to trigger more APs

Reverberatory Network Activity

• neural activity travels in long range loops and does not stay in one cell

• local excitatory networks: neurons mutually stimulate each other

• mutual inhibition: groups of neurons that inhibit one another

Synaptic plasticity

• when stimulus is seen, there is a temporary increase in strength of synapses - higher EPSP

• synapses store info temporarily so that when stimulus is shown again, the neuron is able to fire and remember