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

Memory

Memory is a central component of the brain mechanisms that leads to consciousness. (Edelman; Universe of Consciousness, 93)

Memory is a central functionality that brings together learning, understanding, and consciousness. (Ratey; User's Guide to Brain, 185)

Memories are groups of neurons that fire together in the same pattern each time they are activated. The links between individual neurons, which bind them into a single memory, are formed through a process called long-term potentiation (LTP). (Carter; Mapping the Mind, 176)

All Memory Is Associative

Memories are necessarily associative and never identical. (Edelman; Wider than the Sky, 53)

By the associative property of memory, neural assemblies aggregate via the laws of Gestalts into the sparse but widespread neural assemblies of the dynamic core of consciousness.

Neurons may be connected in a vast associational network, similar to a relational database. (Crick & Koch; Consciousness and Neuroscience, 48)

The enormous associative capabilities of the dynamic core are ideal to link or hierarchically organize a series of preexisting unconscious routines into a particular sequence. Pianist deliberately links separate arpeggio passages. (Edelman; Universe of Consciousness, 187)

Marr (1971) proposed a theory for how the hippocampus could function as an associative memory. From this proposal have followed many extensions, usually focusing on the role of the CA3 recurrent collaterals. (Burgess; Hippocampus Spatial Models, 469)

Relational processing at encoding enables flexible access to information and situations quite different from those of the original learning. (Andersen; Hippocampus Book, 662)

It is suggested that an autoassociation memory implemented by the CA3 neurons enables whole (spatial) scene or episodic memories to be formed. The autoassociation memory described here shows how the episodic memory could be stored in the hippocampus, and later retrieved from the hippocampus and thereby to the neocortex using backprojections. (Rolls; Memory, Attention, and Decision-Making, 41)

Individual memories are formed by the facilitation, or perhaps creation, of synaptic connections between neurons that represent different sensory or motor functions, if and when such features co-occur in the internal or external environment. The temporal coincidence or continuity of attributes, which determines synaptic associations, may be accompanied by spatial contiguity. (Fuster; Memory in Cerebral Cortex, 11)

The informational content of memory networks resides in the associative relationships among the neuronal elements. It is not so much that a memory trace is contained in the network; rather, the memory trace is the network. (Fuster; Memory in Cerebral Cortex, 11)

Autoassociative Network

Neocortex recalls patterns autoassociatively, which means it can recall a complete pattern when given only a partial one. (Gazzaniga; Human, 367)

Individuals with posttraumatic stress disorder (PTSD) typically report experiencing intrusive recollections, nightmares, and distress with physiologic arousal in response to reminders of trauma. (Vogt; Cingulate Neurobiology, 454)

The three brain regions of primary interest in PTSD have been the amygdala, ACC, and hippocampus. (Vogt; Cingulate Neurobiology, 454)

An autoassociator is a self-correcting network that can recreate a previously stored pattern that most closely resembles the current input pattern, even if it is only a fragment of the stored version. (Buzsáki; Rhythms of the Brain, 289)

The main factors that determine the maximum number of memories that can be stored in an autoassociative network are the number of connections on each neuron devoted to the recurrent collaterals, and the sparseness of the representation. (Rolls; Memory, Attention, and Decision-Making, 568)

Amnesic Patient HM

It is important to keep in mind that amnesic patient HM, (see the note at the bottom of this page) who had his hippocampuses removed, retained his declarative memory functionality for short-term memory and his remote long-term memory, but could not form new long-term memories. He could form new procedural memory but retained no knowledge of the learning process.

Major Memory Systems in the Brain

Three major memory systems in the brain. (Eichenbaum; Neuroscience of Memory, 200)

Distinction between Declarative and Procedural Memory

Declarative memory includes Episodic Memory and Semantic Memory.

Procedural memory includes motor skills, cognitive skill learning, simple classical conditioning, priming, habituation, sensitization, perceptual after-effects and other cognitive operations improved by experience. (Squire; Memory and Brain, 164, 170)

Declarative Memory

Two types of declarative memory -- semantic and episodic. (Gazzaniga; Human, 303)

Declarative memory is what most people think of as memory. Declarative memories can be consciously recalled and discussed. There are two kinds: Episodic, Semantic. Episodic memories are all the specific events you have experienced and remembered, and also your associations with people in which you can recall the specific occasion. Semantic memory is all the facts learned in school, ideas learned, mathematical procedures, general recollection of “grandma’s house,” etc.

Distinction between "episodic memory" events tied to specific time and place, as contrasted with "semantic memory" for knowledge that is time- and event-independent. (Eichenbaum; Neuroscience of Memory, 121)

What we normally refer to as the memory of an object is the composite memory of the sensory and motor activities related to the interaction between the organism and the object. (Damasio; Self Comes to Mind, 133)

Memory is not a single entity but is composed of different systems. Only one of these systems is accessible to awareness, the declarative memory system. (Squire & Kandel; Memory, 159)

We perceive what we remember as well as remember what we perceive. (Fuster; Cortex and Mind, 84)

Link to — Declarative Memory as Reconstruction

Long-Term and Short-Term Memory

Functionally, cognitive psychologists make a demarcation between Long-Term Memory and Short-Term Memory.

One of the outstanding challenges to any general brain theory is to explain the structural basis of long- and short-term memory. (Edelman; Neural Darwinism, 204)

Same Brain Areas for Short-Term and Long-Term Memory

Short-term and long-term memory share much of the same cortical substrate and simply reflect different activation states of that substrate. (Fuster; Memory in Cerebral Cortex, 4)

Same brain areas appear to be used for long-term memory as are used for visual perception and intermediate memory. (Squire & Kandel; Memory, 88)

Memory is a normal consequence of perception. (Squire & Kandel; Memory, 91)

Memory impaired patients perform well on tests that make large demands on their perceptual abilities. (Squire & Kandel; Memory, 92)

Link to — Long-Term Memory

Link to — Short-Term Memory

Long-Term Memory

Extended consciousness requires working memory and explicit long-term memory (including both semantic and episodic memories). (Damasio & Meyer; Consciousness Overview, 9)

Distinguish non-consolidated long-term memory and consolidated long-term memory.

Hippocampus-dependent Long-Term Memory

Hippocampus-dependent Long-Term Memories are consolidated as Hippocampus-independent Long-Term Memories

Hippocampus-independent Long-Term Memory

For further discussion of declarative memory involving the hippocampus:

Link to — Memory Consolidatation

Link to — Declarative Memory Classifications

Link to — Memory Encoding

Memory Recall involves a Reconstruction of an Active Neural Network Pattern

Declarative memory is a reconstruction of a prior arrangement of synaptic connections over widely distributed areas of the brain.

A memory is a tiny bit different each time we remember it. (Ratey; User's Guide to Brain, 186)

Memories are retrieved by associative access through their component representations, by reconstruction from fragments. (Fuster; Memory in Cerebral Cortex, 199)

Memory is a replay of neural response patterns adequate to the performance, not some sequence or specific detail. (Edelman; Universe of Consciousness, 98)

Episodic Memory

Episodic memory, the long term recall of sequences of events or narratives, depends on interactions between the hippocampus and the cerebral cortex. (Edelman; Wider than the Sky, 51)

Episodic memory is probably uniquely human. (Andreasen, Creating Brain, 71)

Episodic memory is uniquely human. (Gazzaniga; Human, 303)

Episodic memory is claimed to be uniquely human, a mental travel back in time that endows the individual with the capacity to reference personal experiences in the context of both time and space. (Buzsáki; Rhythms of the Brain, 292)

Episodic memory, enabled by the hippocampal system, is not essential for consciousness. (Carter; Mapping the Mind, 205)

Research work in humans suggests that the hippocampal -- entorhinal system is involved in both episodic and semantic memories. (Buzsáki; Rhythms of the Brain, 327)

Research study — Episodic Memory — Medial Temporal Lobe

Semantic Memory

Semantic memory refers to knowledge of the world. This system represents organized information such as facts, concepts, and vocabulary. (Squire; Memory and Brain, 169)

Semantic knowledge is largely a context-free form of information. It is the "meaning" of things. (Buzsáki; Rhythms of the Brain, 292)

Multiple overlapping observations with common junctions are the source of semantic knowledge. (Buzsáki; Rhythms of the Brain, 330)

The large sector of individual long-term memory that is called semantic memory is widely distributed in the cortex. (Fuster; Memory in Cerebral Cortex, 140)

Language depends largely on semantic memory. (Ratey; User's Guide to Brain, 202)

Semantic memory is usually derived from a learning process.

Link to — Semantic Working Memory System

Short-Term Memory Systems

Cognitive psychologists subdivide short-term memory into two major components: immediate memory and working memory. (Squire & Kandel; Memory, 84)

Because principal neurons frequently discharge in bursts of action potentials, the degree of postsynaptic facilitation or depression during such bursts may contain much of the information transmitted through the network. (Andersen; Hippocampus Book, 211)

Iconic Memory

The shortest of short-term memories is iconic memory, which is the capacity to retain a sensory image or up to one second after presentation. (Fuster; Memory in Cerebral Cortex, 13)

Iconic memory, a high-capacity, rapidly-decaying visual form of storage, is quickly established and persists for at least a few hundred milliseconds. (Koch; Quest for Consciousness, 201)

The existence of iconic memory is well-established experimentally. (Crick & Koch; Consciousness and Neuroscience, 38)

One of the functions of iconic memory is to provide sufficient time to allow the brain to process brief signals. (Koch; Quest for Consciousness, 202)

Koch believes that iconic memory is necessary for visual perception. (Koch; Quest for Consciousness, 202)

Iconic memory is probably instantiated throughout the visual brain, starting as early as the retina and including the various cortical areas and their associated thalamic nuclei. (Koch; Quest for Consciousness, 202)

Iconic memory's neuronal substrate is the afterglow left by the waves of spikes sweeping up the visual hierarchy, amplified by local and more global feedback loops. (Koch; Quest for Consciousness, 204)

Immediate Memory

Immediate memory would last a few seconds longer than iconic memory. It coincides of what is commonly understood as short-term memory. (Fuster; Memory in Cerebral Cortex, 13)

Working Memory — Summary of Baddeley’s Working Memory Model

Baddeley’s working memory model assumes a four component system, comprising (1) an attentional controller, the central executive, and three temporary storage systems:(2) the visuospatial's sketch pad, (3) the phonological loop, and (4) a more general integrated storage system, the episodic buffer. (Baddeley; Working Memory, 13)

Working memory, a concept of short-term memory, is essentially a temporary storage used in performance of cognitive behavioral tasks. (Fuster; Memory in Cerebral Cortex, 14)

Short-term retention of information in working memory is supported by sustained activity in cortical regions whose primary function is not working memory. (Postle; Activated Long-Term Memory, 344)

Attention and working memory are closely intertwined, making it difficult to cleanly separate them. The more working memory is taxed, the less effective attention is at disregarding distractors. (Koch; Quest for Consciousness, 197)

Working memory appears to go hand-in-hand with consciousness. (Koch; Quest for Consciousness, 199

Central Executive

Central executive of working memory controls access to the phonological loop, visual buffer, temporary storage for other modalities, via a sort of attentional selection process. (Koch; Quest for Consciousness, 197)

Neuroimaging studies have suggested that the executive attentional control system is located in the prefrontal cortex, predominantly in the dorsolateral prefrontal cortex (DLPFC) and the anterior cingulate cortex (ACC). (Osaka; Neural Bases of Focusing Attention, 100)

Visuospatial Sketchpad

One short-term memory system is in dorsolateral prefrontal cortex, Brodmann area 46. This is involved in remembering the locations of spatial responses. (Rolls & Treves; Neural Networks, 246)

Phonological Loop

Phonological loop component of working memory was originally developed to account for four memory phenomena -- (1) word length effect, (2) acoustic confusion effect, (3) irrelevant speech effect, (4) concurrent articulations effect. (Neath; Working Memory Phonological Loop, 165)

Episodic Buffer

Episodic buffer is a limited capacity temporary storage system that integrates information from a number of sources across space and time. (Martin; Cognitive Neuropsychology, Working Memory, 184)

Memories are Hierarchical

Memories are stored hierarchically through association areas of parietal and temporal through to frontal cortex. Each memory is reconstructed as a sparse, active neural network pattern. Individual neurons are reused in different memories, each dendritic tree having a different pattern of active synapses for each individual memory.

Given that most memories are essentially hierarchical, made up of cognitive contents of different hierarchical levels, and given that the memory contents at one level are better consolidated than those at another, not all contents of a memory are equally retrievable. (Fuster; Cortex and Mind, 133)

Recency Effect

Ability to discriminate among memories decreases as the memories become more remote. (Baddeley; Working Memory, 106)

Recency effect is one of the most stable and reliable phenomena within the study of human memory. (Baddeley; Working Memory, 115)

Recency effect is what allows us to orient ourselves in time and space. (Baddeley; Working Memory, 115)

Procedural Memory

Procedural memory includes motor skills, cognitive skills, simple classical conditioning, habituation, sensitization, and other cognitive operations improved by experience. (Squire; Memory and Brain, 170)

Emotional Memory

Emotional memories are not stored in the amygdala directly but are stored in the cingulate and parahippocampal cortices, with which the amygdala is interconnected. (Kandel; Principles of Neural Science, 992)

The role of the OFC in emotional memory. (Zald & Rauch; Orbitofrontal Cortex, 69)

The hippocampus and amygdala likely interact in the formation of emotional memories. (Vogt; Cingulate Neurobiology, 455)

Amygdala connected to sensory processing systems and to motor control regions - (diagram) (LeDoux; Synaptic Self, 62)

Projections of the amygdala to the cortex are considerably greater than the projections from the cortex to the amygdala. (LeDoux; Emotional Brain, 284)

Plasticity within the amygdala pathways supports emotional memory in the absence of conscious recollection. (Eichenbaum; Neuroscience of Memory, 280)

Visual, acoustic, and olfactory stimuli associated with a highlycharged emotional situation take on the affective qualitiesof that situation. (Emotional Memory Storage, Science 6 August 2010)

Central and basal nuclei of the amygdala send a broad range of outputs back to cortical areas, to subcortical areas involved in other memory systems and behavior, and to autonomic system and brainstem outputs for the expression of emotion through a variety of systems. (Eichenbaum; Neuroscience of Memory, 280)

The basolateral amygdala (BLA) has a crucial role in emotional learning irrespective of valence. (Amygdala to Nucleus Accumbens Pathway, Nature 475, 377–380, 21 July 2011)

Amygdala receives inputs from the inferior temporal visual cortex, but not from earlier stages of cortical visual information processing. (Rolls & Treves; Neural Networks, 146)

The amygdala also receives inputs that are potentially about primary reinforcers, for example taste inputs (from the secondary taste cortex, via connections from the orbitofrontal cortex to the amygdala). (Rolls & Treves; Neural Networks, 146)

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Profound Influence on Memory Research

HM Died (New Tork Times, 4 Dec 2008)

Henry Gustav Molaison (1926-2008)

In 1935, when Mr. Molaison, at 9 years old, he banged his head hard after being hit by a bicycle rider in his neighborhood near Hartford, CT.

In 1953, eighteen years after that bicycle accident, Mr. Molaison arrived at the office of Dr. William Beecher Scoville, a neurosurgeon at Hartford Hospital. Mr. Molaison was blacking out frequently, had devastating convulsions and could no longer repair motors to earn a living.

After exhausting other treatments, Dr. Scoville decided to surgically remove two finger-shaped slivers of tissue from Mr. Molaison’s brain. The seizures abated, but the procedure — especially cutting into the hippocampus, an area deep in the brain, about level with the ears — left the patient radically changed.

Alarmed, Dr. Scoville consulted with a leading surgeon in Montreal, Dr. Wilder Penfield of McGill University, who with Dr. Brenda Milner, a psychologist, had reported on two other patients’ memory deficits.

In 1962 Dr. Milner presented a landmark study in which she and H. M. demonstrated that a part of his memory was fully intact.

Scientists saw that there were at least two systems in the brain for creating new memories. One, known as declarative memory, records names, faces and new experiences and stores them until they are consciously retrieved. This system depends on the function of medial temporal areas, particularly the hippocampus.

H. M.’s short-term memory was fine; he could hold thoughts in his head for about 20 seconds. It was holding onto them without the hippocampus that was impossible.

“The study of H. M. by Brenda Milner stands as one of the great milestones in the history of modern neuroscience,” said Dr. Eric Kandel, a neuroscientist at Columbia University. “It opened the way for the study of the two memory systems in the brain, explicit and implicit, and provided the basis for everything that came later — the study of human memory and its disorders.”

Living at his parents’ house, and later with a relative through the 1970s, Mr. Molaison helped with the shopping, mowed the lawn, raked leaves and relaxed in front of the television. He could navigate through a day attending to mundane details — fixing a lunch, making his bed — by drawing on what he could remember from his first 27 years.

Henry Gustav Molaison, born on Feb. 26, 1926, left no survivors. He left a legacy in science.

Link to a Synopsis of HM’s Injury and Follow-up Research

Link to my copy of the New York Times H.M. obit.

Link to — Memory — Recent Research

Return to — Perception, Memory, Consciousness

Link to — Consciousness Subject Outline

Further discussion — Covington Theory of Consciousness