PrefrontalCortexReview
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Neuroscience findings overview and implications from book by Joaquin Fuster - The Prefrontal Cortex
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Below are most interesting thoughts, from my point of view, of monography by Joaquin Fuster about anatomy, chemistry, physiology and other aspects of prefrontal cortex, inferring that prefrontal cortex in human makes integrative role and mediating temporal contingency.
Chapter 1. Introduction
- cortex of anterior pole of mammalian brain is commonly designated the prefrontal cortex (PFC)
- other terms, less convenient: frontal granular cortex and frontal association cortex
- frontal lobe = PFC + motor cortex (MC) + premotor cortex (PMC)
- in book defined as part of cerebral cortex that receives afferent projections from mediodorsal nucleous of thalamus (TH)
- PFC is connected to many other cerebral structures
- there is certain synergy in PFC functions
- basic functions of PFC are few
- these functions are interrelated, mutually supporting in purposive behavior
- cognitive and emotional functions are integrative and goal-directed
- PFC is action cortex
- skeletal, ocular
- expression of emotion, speech, visceral control
- internal mental action - reasoning
- posterior cortex (PC) is sensor cortex
- PFC does nothing by itself
- in cooperation with other cortices, subcortical structures
- action domains - specialization of of action within PFC
- in evolution PFC grows in relative size on par with functional role - reaches maximum in human
- cognitive parts (lateral) grows greater than emotional (orbital, medial)
- any series of purposive actions, that deviates from rehearsed automatic routine, requires functional integrity of lateral PFC (LPFC)
- the longer the series, the greater is the need
- other factors include complexity and novelty of actions, uncertainties and ambiguities in source information
- time is the single most important attribute placing complex and novel sequence under physiological purview of PFC - to organize actions in time domain
- with - new, acquired, elaborate behavior, speech fluency, higher reasoning, creative activity with more than minimal temporal dimension
- without - only instinctual or automatic routine
- all cortical functions take place on neural substrate, repository of permanent, modifiable by experience long-term memory (LTM)
- neural substrate of PFC - networks of executive memory, which extend into other cortical areas
- all executive functions of LPFC are determined by goals
- major feature of LPFC - ability to structure the present in order to serve the future
- executive functions utilize neural substrate:
- for acquisition of further executive memory
- for organization of behavior, reasoning and language
- for executive attention
- executive attention has 3 components for temporal organization of action:
- working memory
- preparatory set
- inhibitory interference control
- none are localized in PFC, but all need PFC to operate
- working memory is memory in active state
- different from "short-term memory" (STM), which is precursor for LTM
- working memory is temporary activation of updated LTM networks for organizing actions in the near term
- sustained attention focused on internal representation
- engages LPFC and PC - cognitive control
- preparatory set is priming sensory and motor neural structures (motor attention) for performance of act contingent on prior event
- engages LPFC and structures below PFC in hierarchy of motor structures - e.g. PMC, basal ganglia (BG) - also part of cognitive control
- temporally opposite to working memory - both mediate cross-temporal contingencies
- inhibitory control - enhances and provides contrast to excitatory functions
- selective attention is accompanied by suppression o of cognitive or emotional contents or operations, interfering with attention
- in PFC sensory inputs or motor or instinctual impulses that might impede or derail actions are held in check
- mainly represented in orbitomedial PFC (OMPFC)
- OMPFC is involved in reward, contains important components of neurotransmitter systems activated by biological and chemical rewards
- PFC areas specialize in different sub-functions of temporal organization and different forms of action (action domains)
- principles of the book:
- all PFC areas and functions are to some degree interdependent
- various functions share areas and networks in common
- temporal organization of complex and novel actions toward their goal is product of neural dynamics of perception-action cycle, which consists of coordinated participation of neural structures in successive interactions of organism with environment in pursuit of goals
- cerebral cortex is on top of cycle with signals through hierarchically organized neural channels
- internal signals into OMPFC, external signals into LPFC
- at each hierarchical level of the cycle there is feedback to prior levels
- at highest level, there is reentrant feedback from PFC to PC
Chapter 2. Anatomy of the Prefrontal Cortex
Evolution and comparative anatomy
- PFC occupies 29% in human, 17% in chimpanzee, 7% in dog, 3,5% in cat of total cortex - greatest mgnitude
- human PFC is substrate for cognitive functions of highest order
- PFC is defined by topology, topography, architecture and fiber connections
- in mammals emerged and developed between hippocampus and piriform area
- in primates emerged from 3 fields - parahippocampal, parapiriform in cingular area and motor cortex (MC)
- PFC with evolution becomes more complex, fissurated and involuted
- PFC folds and gains surface with 3-d expansion of subcortical masses
- gyri and sulcus separate areas of different functional significance
- large expansion of presilvian area is one of most remarkable in evolution
- granularization of layer 4 is characteristic of primates prefrontal cortex
- connections between PFC and mediadorsal nucleus of TH are organized topologically
- in higher species cortico-cortical connections have great functional importance
- cortical neuronal networks are the essence of cognition
- in primate mediodorsal projection coincides with granular cortex
