Scientific Understanding of Consciousness
Consciousness as an Emergent Property of Thalamocortical Activity

Prefrontal Cortex

Prefrontal cortex is a convergence zone; receives connections from various specialized regions (visual, auditory, etc.); receives connections from hippocampus and other cortical areas involved in long-term explicit memory; retrieve stored information. (LeDoux; Synaptic Self, 180)

Prefrontal cortex is one of the most richly connected regions of the cerebrum. (Fuster; Memory in Cerebral Cortex, 295)

Prefrontal regions are reciprocally connected with temporal, parietal, and occipital cortices, where they receive higher-level visual, auditory, and somatosensory information. (Miller; Human Frontal Lobes, 49)

Prefrontal regions have strong connections with limbic structures such as the hippocampus and amygdala, which mediate processes such as learning and memory, emotional and affective tone, autonomic regulation, drive, and motivation. (Miller; Human Frontal Lobes, 49)

Prefrontal cortex sends connections to areas involved in movement control (frontal cortex and subcortical regions), allowing executive decisions to be converted into voluntary actions. (LeDoux; Synaptic Self, 180)

Connections within the prefrontal cortex, both within and between layers, are far more numerous than the connections coming in from other areas, such as sensory processing areas. (LeDoux; Synaptic Self, 188)

 

Research Study — Memory Consolidation Engrams and Circuits

Research Study — Brain Regions Involved in Decision-Making

Research Study — Prefrontal Cortex Human Reasoning

Research Study — Context-dependent computation by recurrent dynamics in prefrontal cortex

 

Visual System Anatomy and the Synaptic Connections of Working Memory

Prefrontal cortex -- this is the only part of the brain that is free from the constant labor of sensory processing. (Carter; Mapping the Mind, 182)

Studies of visual processing, combined with the vast amount of knowledge about anatomical connections and functions of the visual system, have helped construct a fairly detailed understanding of the synaptic connections underlying working memory. (LeDoux; Synaptic Self, 180)

Dorsolateral prefrontal cortex -- things are held in mind here and manipulated to form plans and concepts.  This area seems to choose to do one thing rather than another. (Carter; Mapping the Mind, 182)

 

Lateral Prefrontal Cortex, Unique to Primates

The evolutionarily newest region of the prefrontal cortex, lateral prefrontal cortex is apparently unique to primates and is concerned mainly with the rational aspects of decision-making, which are our conscious efforts to reach a decision. (Gazzaniga; Human, 21)

The original two regions of prefrontal cortex, which are present in other mammals and evolved earlier, are the orbital prefrontal region, which responds to external stimuli that are likely to be rewarding, and the anterior cingulate cortex, which process information about the body's internal state. (Gazzaniga; Human, 21)

Orbital prefrontal region and the anterior cingulate cortex, the two original regions of prefrontal cortex work together to contribute to the emotional aspects of decision making. (Gazzaniga; Human, 21)

 

Working Memory in Prefrontal Cortex

Working memory is mediated by neural networks in the prefrontal cortex (PFC). - (diagram) (LeDoux; Synaptic Self, 181)

Working memory functions are not located in a single region of prefrontal cortex but are distributed across widespread regions. (LeDoux; Synaptic Self, 192)

Damage to the human prefrontal cortex disrupts the conscious retrieval of long-term memories, especially episodic memories. (LeDoux; Synaptic Self, 192)

Explicit conscious memory: (1) involvement of medial temporal lobe, (2) conscious of the information at the time of the original experience, (3) during retrieval, must transfer the information from cortical storage areas into working memory. (LeDoux; Synaptic Self, 192)

 

Prefrontal Cortex and Working Memory — Eichenbaum explains that while the entire cerebral cortex is involved in memory processing, the chief brain area that mediates these processes is the prefrontal cortex.

 

Dopamine in Prefrontal cortex

Prefrontal cortex receives a rich supply of axons containing dopamine. (LeDoux; Synaptic Self, 189)

Dopamine participates in working memory by biasing cells to mainly respond to strong inputs and thereby focusing attention on active current goals and away from distracting stimuli. (LeDoux; Synaptic Self, 189)

Dopamine cell bodies are located in the ventral tegmental area of the brain stem. Axons of these cells branch extensively into the forebrain where the terminals release dopamine. (LeDoux; Synaptic Self, 189)

Dopamine receptors located on the spines and shafts of dendrites of excitatory cells seem to reduce the transfer of excitation from the dendrites to the cell bodies, allowing only especially strong excitatory inputs to elicit excitation. (LeDoux; Synaptic Self, 189)

Dopamine cells in the brain stem modulate all aspects of the circuitry in the prefrontal cortex, enhancing or facilitating the excitation. (LeDoux; Synaptic Self, 190)

Extensive excitatory connectivity in the prefrontal cortex, together with its enhancement by dopamine, might underlie the ability of working memory to hold stimuli as long as the organism remains engaged in the task. (LeDoux; Synaptic Self, 190)

Output of motor systems inhibits dopamine cells, suggesting that once behavior is produced, the facilitation by dopamine terminates, and working memory is released to do other things. (LeDoux; Synaptic Self, 190)

 

Prefrontal Cortex

Prefrontal cortex performs its cognitive role in cooperation with orbitomedial and posterior association cortices, the striatatum, and other subcortical structures. (Fuster; Prefrontal Cortex, 379)

Prefrontal cortex takes part in all decisions, although its lateral regions are mainly involved in rational factors, whereas its medial and orbital regions of mainly involved in emotional factors. (Fuster; Prefrontal Cortex, 191)

Entire prefrontal region seems dedicated to categorizing contingencies. Different domains of knowledge are categorized in different prefrontal sectors. (Damasio; Descartes' Error, 182)

Bioregulatory and social domain have affinity for the ventromedial sector. (Damasio; Descartes' Error, 183)

Domains that subsume knowledge of the external world align with the dorsolateral region. (Damasio; Descartes' Error, 183)

Prefrontal cortices are directly connected to every avenue of motor and chemical response available to the brain. Dorsolateral and upper medial sectors can activate the premotor cortices and from there, the primary motor cortices, the supplementary motor area, and the third motor area. (Damasio; Descartes' Error, 183)

Multiple areas in the dorsolateral prefrontal cortex, in particular areas 8, 46, 12, and 45, play an essential role in what has been termed memory-guided performance. (Goldman-Rakic; Circuit Model of Working Memory, 131)

 

Research Study — Prefrontal Cortex (PFC) tuned to Mixtures of Multiple Task-Related Aspects

 

Ventromedial Cortex

Ventromedial cortex is the brain's emotional control center.  It is exceptionally active during bouts of mania, and inactive during depression. (Carter; Mapping the Mind, 197)

Connections between the ventromedial cortex and the limbic system beneath it are very dense, closely binding the conscious mind with the unconscious. (Carter; Mapping the Mind, 197)

The connections between the ventromedial cortex and the limbic system has a special status -- this region best incorporates the whole of our being, making sense of our perceptions and binding them into a meaningful whole. (Carter; Mapping the Mind, 197)

Area of the brain that is most noticeably affected in both depression and mania is an area on the lower part of the internal surface of the prefrontal cortex -- the ventromedial cortex. (Carter; Mapping the Mind, 197)

 

Research study — Social Decisions in the Ventromedial Prefrontal Cortex

Research study — Intracranial Markers of Conscious Access

 

Link to — Perception-Action Cycle

Link to — Reentry and Recursion

 

Subcortical motor machinery of the basal ganglia is accessible to the prefrontal cortices. (Damasio; Descartes' Error, 183)

Ventromedial prefrontal cortices send signals to autonomic nervous system effectors and can promote chemical responses associated with emotion out of the hypothalamus and brain stem. (Damasio; Descartes' Error, 183)

Prefrontal cortices, particularly the ventromedial sector can acquire a three-way link between (1) body state, (2) the individual's unique experience, (3) effectors of those body states. . (Damasio; Descartes' Error, 183)

 

Research study — Prefrontal Cortex Functionally Compartmentalized

Research study — Modularity of Categorization in Parietal Cortex

 

 

Anatomy of the prefrontal cortex

(paraphrase of Eichenbaum, Cognitive Neuroscience of Memory, 313ff)

The assignment of the central executive function to the prefrontal cortex is supported by substantial anatomical data. The phenomenal expansion of the prefrontal area in primates and especially humans is impressively associated with the evolution of cognitive capacities. The prefrontal cortex in humans is a diverse area, composed of several distinct subdivisions. There is considerable consensus on correspondences in monkeys with identified areas in the human prefrontal cortex. Although several anatomical areas have been characterized based on morphological ap­pearance, most of the functional evidence has been related to four general regions. These include the medial, dorsolateral, ventrolateral, and orbital areas. Most of the attention with regard to working memory functions in monkeys and humans has focused on the dorsolateral and ventrolateral areas, and these areas are partially distinct in their connections with more posterior parts of the cerebral cortex. Each of the subdivisions receives input from a diverse set of rostral and causal cortical areas, and each has a distinctive input pattern.

In addition, prefrontal areas are characterized by considerable asso­ciative connections with other prefrontal areas. Nevertheless, despite this diversity and associativity with the prefrontal cortex, a few generalities have emerged about distinctions among prefrontal areas with regard to their inputs from posterior cortical areas. Thus, in general, the dorsolat­eral prefrontal area receives inputs mainly from medially and dorsolaterally located cortical areas that preferentially represent somatosensory and visuospatial information. Conversely, in general, the lateral prefrontal areas receive inputs mainly from ventrolateral and ventromedial cortical areas that represent auditory and visual pattern information. In particular, the differentiation of visuospatial input to the dorsolateral prefrontal area, and visual pattern input to the lateral prefrontal area has received considerable attention in studies on distinct working memory systems.

There is considerable agreement that different posterior cortical areas are activated during modality-specific working memory processing. On the other hand, there is considerable controversy over whether different kinds of processing are parcellated within the prefrontal cortex, and about the nature of parcellation.

 (end of paraphrase )

 

 

Return to — Working Memory

Return to — Frontal Lobes

Link to — Consciousness Subject Outline

Further discussion -- Covington Theory of Consciousness