Greg Detre
Wednesday, 24 May, 2000
Rolls � B&B III
prefrontal = cortex of the anterior pole of the mammalian brain
whatever the criteria for tracing its boundaries, no demarcation can be said to outline a structural entity with unitary function
on morphological grounds alone: thanatomical complexity (especially in higher animals), makes its functional homogeneity implausible
behavioural study of animals with selective lesions of this cortex �/span> rules out such homogenity
untiary role: also inconsistent with clinical findings in patients with injuries to this part of the brain
large number of diverse + seemingly unrelated facts � apparently multiople functions � but het basic funcitons seem to be essentially few, and are represented over the cortical surface according to a certain topological pattern
interrelated, mutually supporting and complementing functions in the purposive behaviour of the organism
prefrontal � ugly, misuses �pre�, aka frontal granular cortex (cytoarchitectonic features in primates) and frontal association cortex (ambiguities of the word �association�)
often referred to as �frontal�, implicitly excluding the motor and premotor areas
in rodents and carnivores, is also called the �orbitofrontal cortex�, easily confused with �orbital frontal cortex� (which in primates = the ventral aspect of the frontal lobe which forms part of the prefrontal cortex)
defined as the part of the cerebral cortex that receives projectisons from the mediodorsal nucleus of the thalamus (applicable to all mammalian brains)
unitary function � but at different levels
primates: cerebral cortex of both hemispheres is divided by the central sulcus (Rolandic fissure) into 2:
posterior � sensation, perception, perceptual memory
frontal � action and motor memory
both are hierarchically organised in terms of development, connectivity, memory and processing of sensory and motor information
dorsal and lateral frontal cortex � segregated action domains for:
� skeletal movement
� eye movement
� speech
actions are represented by increasing order of complexity + novelty in higher interconnected areas
abstract schemas = gestalts of actions + goals; novel plans, structures of behaviour
automatic + routine actions are represented in lower levels of motor hierarchies
plans: motor hierarchy in the dorsolateral frontal cortex:
connectivity flows downwards from prefrontal � premotor � premotor
all stages within each action domain are reciprocally connected, as well as with each other through subcortical loops through the basal ganglia
sequential action: parallel + serial processing
orbitomedial frontal cortex � action domain for emotional behaviour + visceral manifestations
transmits information of limbic origin about the internal milieu � dorsal cortex
plays a role in decision-making
important cortical depository of emotional memory
frontal lobe cortex � initation and execution of deliberate actions
�executive� functions � decision-making, attention, planning and working memory
= phenomena of neural processing, without unique locations of their own
organism�s basic drive + motivations
arrive in frontal cortex from diencephalic and limbic formations
other inputs from sensory receptors and areas of the posterior cortex
attention = ability to select sensory inputs and actions, and to inhibit others
widely distributed in the frontal cortex
dorsolateral = selective
orbital = exclusionary/inhibitory
perception-action cycle = circular flow of organism-environment interactions
sensory processing + consequent action
in cognitive + emotional behaviour
highest level: cycle completed by reciprocal connections between posterior association and prefrontal cortex
prefrontal � mediates cross-temporal contingencies
i.e. bridges time gaps in a structure of behaviour
3 temporal integrative functions of the prefrontal cortex:
= the provisional retention of (sensory or motor) information for prospective action
mainly a function of the action domains of the dosolateral prefrontal cortex
maintained active in neuronal networks by reverberation through reentrant circuits
i.e. motor attention = selection of particular motor acts (from an established repertoire of motor memory) and preparing the sensory/motor systems for them
essential for execution of plans (temporally extended set)
also based in the dorsolateral prefrontal corte � though probably under influences from the anterior medial cortex
exclusionary role of attention
i.e. protects behavioural structures from external/internal interference (e.g. similar but inappropriate sensory/motor memories)
based primarily in the orbitmedial prefronal cortex � exerted on a variety of cortical + subcortical regions
dorsal vs lateral frontal cortex