The PFC is anatomically well situated to play a role in cognitive control. It receives information from and sends projections to sensory systems, motor system structures that produce voluntary movement, systems that consolidate long-term memories, and systems that process information about affect and motivational state. This anatomy long has suggested that the PFC may be important for synthesizing external and internal information needed to produce complex behavior. Unlike electrical stimulation of more posterior regions that produce hallucinations or motoric responses, stimulation of the PFC produces no obvious effect. This led it to be termed silent cortex.
Effects of Damage to PFC in Humans Often the effect of damage is not obvious. More subtle aspects of behavior – loss of cognitive control - poor judgment, Irresponsible, impulsive Emotional impairments Action disorganization syndrome General – problems with goal directed behavior Phineas Gage Damasio: Descartes’ Error Link between rational behavior and affect
Inhibition of word perseveration Organization of behavior Activates vlPFC Stroop effect Wisconsin card sorting task Tower of Hanoi
Orbitofrontal ctx Activated by rewards – even abstract such as money Food rewards – only if a decision is involved eg ordering from a menu Lateral PFC – more cognitive tasks such as Stroop Ventrolateral – more involved with tasks requiring working memory Dorsolateral – more involved with tasks requiring use of information fMRI evidence
Localized lesions in monkeys: Double Dissociation: A monkey with lesion X must be impaired at process A, but not process B, and a monkey with lesion Y must be impaired at process B, but not process A. Implies X necessary for process A, Y necessary for B single dissociation, eg lesion X impairs process A, but not process B, is insufficient evidence because this could be achieved simply because the test to assess A is more sensitive than the test used to assess process B.
Dorsolateral PFC – impairments in delayed spatial response task Ventrolatral – deficits in delayed match to sample Orbital – impaired at spatial reversal tasks And object reversal tasks (C and D) Localization of function is weak Eg task in E shows impairments in DLPF lesions although no obvious spatial component Object self-ordered task
Neurons are activated by visual, auditory, tactile, and gustatory stimulation (and their memory) as well as voluntary limb and eye movements. Neural recordings from PFC Task demands can exert a strong modulatory influence on PFC activity, consistent with its putative role in cognitive control
Cells respond during a delayed spatial response task
DLPFC – cells have tuned responses to remembered locations. Response depends on dopamine. Consistent with role in organization of goal directed behavior
Delay activity is robust to intervening distractor stimuli (unlike sensory cortex) Delay activity thought to be mediated by loops through the basal ganglia and to depend on dopamine. Local injection of DA antagonists in the PFC blocks delay activity in the PFC.
Cells exhibit rule specific activity. Activity of 4 cells when a particular object cues either a leftward or rightward saccade. Cell responds when images cues a rightward Response but not when the same image is used In a match to sample task.
PFC cells are rapidly adaptable Monkeys can learn new conditional visuomotor associations in just a few trials and PFC cell activity reflects the new associations. Eg FEF cells rapidly learn to search for a particular target – eg red stimulus. PFC cells encode reward information eg some neurons are activated by the delivery of a reward, others respond when an expected reward is not delivered. PFC neurons also encode the type of reward that the monkey expects to receive, Eg cabbage versus a raisin, as well as the quantity of reward the monkey expects. Further, the neurons appear to encode the monkey’s relative preference for the rewards that are available, rather than some absolute measure of reward.