The Evolution of Memory Systems

The Evolution of Memory Systems – Murray, Wise and Graham – Oxford University Press - 2017

Key Points This is a neurosciences, cognitive neuropsychology/ physiology perspective. It takes a forensic view of the anatomical and evolutionary development of observed memory manifestations. It posits that “Memory Systems store information” (as computer analogue). And “Human Brains can generate Representational Systems based on stored memories”

Their Proposition Their Evolutionary Accretion Model of Memory proposes that:

Early vertebrates used one of their innovations (adaptations?), the Telencephalon*, along with sensory receptors concentrated in their heads, to guide mobile, predatory foraging and defence.

(*The anterior part of the primitive forebrain, or prosencephalon, which develops into the cer ebral cortex, olfactory bulbs, and basal ganglia.)  

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This Telencephalon included a homologue of the Hippocampus, which housed a navigation system that stored and used cognitive “maps”. At first, this navigation system functioned mainly in concert with the older reinforcement systems, which guided behaviour by linking stimuli and actions to biological costs and benefits (Adams risk thermostat). Later, several new representational systems evolved, each of which, reflected the adaptations of a specific ancestor (sequentially, incrementally?); and When the newest one (the social subjective system) began to interact with older ones, humans developed the kind of memory that involves the perception of knowing facts and participating in events. All cortical areas store memories based on their specialised representations. These include the so called “medial temporal lobe”. The prefrontal cortex and the anterior temporal lobe contribute to explicit memory. The basal ganglia supports each representational system as a component of cortex basal ganglia loops. This archetypal telencephalonic architecture evolved early in the history of vertebrates. Many cortical areas function in both perception and memory. Modern humans have inherited several (at least seven) representational systems, each of which evolved in the distant past as a specific ancestor adapted to a way of life. Explicit memory does not arise from any one of these systems. Instead, this uniquely human trait depends on interactions between species specific re-representations of self and other representational systems, including a navigation system that evolved early in the history of vertebrates. A sense of experiencing events and knowing facts results from these interactions. When – sometime during hominin evolution – episodic and semantic memories combined with “explosive generalisation” across cognitive domains, our ancestors developed rich autobiographical narratives; a repository of conceptual innovation that characterises modern humans.

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They disparage the current prevailing views and outdated models such as Maclean’s Triune model, as   

it seems too simplistic and misleading (mis-assigns brain processes and structures to functions which developed much earlier) and They don’t buy interfering levels from previous structures (Lizard Brain), although they do buy interacting (interfering?) functional centres in memory processes. They prefer simple linear process model of operations (not emergent?)

History and Evolution Henry Molaison (HM) had severe epilepsy; and during diagnosis his memory was tested extensively. In 1953 they operated and removed much of his Hippocampus,   

He then lost the ability to remember newly learned facts (Antegrade memory). He could still learn motor and perceptual skills and briefly remember short term. He could remember the distant past.(Retrograde memory)

They propose that – “people incorporate representations of themselves into memories”. HM (Henry Molaison) could not do that. Early experiments with monkeys could not reproduce HM symptoms and failed to recognise that human and monkey brains are different! (A Species difference which evolved). Based on these observations the “prevailing view” (which they diverge from) of memory, identified these properties (different abilities) with specific functions and structures. Table 1 Prevailing view of Memory (After Murray et al) Memory system

Brain Structure

Habits Basal Ganglia Explicit Memory Medial Temporal Lobe Emotional Conditioning Amygdala Motor Conditioning Cerebellum Priming* Cerebral Cortex *Priming involves implicit, non-declarative and procedural memories. Oher brain structures responsible for perception, motor control, executive functions, attention, etc. do not seem to be involved – why not? The answer lies in history. 1. The evolutionary History, and 2. The Intellectual History

Anatomy and Physiology The prevailing view (each part of the medial temporal lobe acts cooperatively to provide in turn each of these required memory processes) does not adequately address / explain observations. The evidence (and functional brain imaging), suggests that each part performs a different function, some of which are opposing actions. Also other brain structures (prefrontal cortex and anterior temporal lobe) contribute as well.

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They ask three questions:A. Which representational systems evolved? B. When and in what kind of animal? C. Why? – What adaptive advantage did it confer? In answer to A they recognised (suggested/postulated) that seven separate systems had evolved: Reinforcement Memory – stimuli associations Navigation Memory – a cognitive map for orientation. Biased Competition Memory – top down direction of competing representations. Manual Foraging Memory – makes choices between visually guided movements. Feature Memory – gives sensory dimensions and attributes and metrics - places, numbers, likelihood, speeds, order, distances and durations. 6. Goal Memory – objects and targets of actions and behavioural options and associations. 7. Social Subjective Memory – representation of self and others, offering underlying social knowledge and self-reflection. 1. 2. 3. 4. 5.

For B they identified the evolution / emergence of these different systems, as when:1. Very early as animals became mobile and needed to know (and remember by reinforcement function – Pavlovian?) when, where and how to move. 2. Early vertebrates developed this cognitive map function (as the telencephalon), for guiding movements. 3. Early mammals developed the cortex and this enabled the Biased Competition function. 4. In early primates, a suite of new cortical areas were available for storing memories on how to find, evaluate, grasp, manipulate and draw on old representations for appropriate responses.(Foraging Function) 5. And 6. Continuous evolution to anthropoid primates enabled Goal and Feature functional ability. 6. The Social subjective (function?)/ memory became a necessary human attribute. For C. they identified why as:      

Reinforcement – organisms crucially need nutrients, but must avoid accidents, dangers to attain rewards (Adams risk thermostat?) Navigation – this allowed information from remote (in the organism’s body) sensors (Optical, Olfactory, etc.) to be collated as a reference “map” of the local environment. Biased competition - regulated conflicting representational cues for appropriate situations (from memory) Manual Foraging – Tactics needed for hunter gathering (a generic animal trait?) Feature – needed for the sophisticated primate vision systems Goal – generates goals from abstract strategies. Social subjective – species specific representations of “self”. Confers far reaching emergent properties as adaptations to social systems.

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Table 1.2 The Evolutionary Accretion (additions over time) Model. Memory System

Ancestor

Brain Structures

Reinforcement Navigation Biased Competition Manual Foraging

Early Animals Early Vertebrates Early Mammals Early Primates

Feature

Anthropoids

Goal Social Subjective

Anthropoids Hominins

Various* Hippocampal Complex Agranular prefrontal cortex Posterior Parietal, inferior temporal, And granular prefrontal cortex Posterior parietal, inferior and superior temporal, And perirhinal cortex Granular prefrontal cortex Granular prefrontal cortex

*Basal Forebrain, extended basal ganglia, extended amygdala, dopaminergic neurons, cerebellar cortex, deep cerebellar nuclei, and inferior olivary nuclei, among other structures.

Table 1.3 Contrasts between the two views of Memory Topic

Prevailing View

Evolutionary Accretion Model

Function of cortical Area

Some areas function in memory, others in perception, and still others in “executive”, or motor control Four cortical areas called the “Medial Temporal Lobe”

All areas function in memory, using specialised representations

Substrate of explicit (declarative) memory Substrate of implicit (nondeclarative) memory Evolution

The basal Ganglia as a whole

Habits and the basal ganglia evolved in “reptiles”, explicit (declarative) memory and the limbic cortex evolved in “primitive” mammals.

Interactions between the navigation, feature, goal and social subjective systems Cortex based ganglia “Loops” that have weak links to social subjective memories New specialised representations emerged as five specific ancestral species adapted to a new way of life in their time and place.

Summary The telencephalon originated in early vertebrates (other animals don’t have it, all known vertebrates have it): along with new embryonic tissues that produced the head and its sensory organs, including paired eyes. These animals, used information detected at a distance, in large part provided by vision and olfaction, to guide foraging and self-defence. The Telencephalon exerted control over the body through its connections with the motor system, broadly construed to include the neuroendocrine, neurosecretory and autonomic outputs, as well as skeletal and eye muscles. (See fig 1 below). 4 FRMBRNds0.1

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Through interactions with the hypothalamus, the telencephalon of early vertebrates regulated metabolism and maintained homeostasis. Through interactions with hypothalamus, brainstem and spinal cord, it also controlled reproductive, ingestive, exploratory and defensive behaviours mediated by skeletal muscles. Of most relevance to memory systems, the telencephalon that emerged in early vertebrates included homologues of both the hippocampus and the basal ganglia. With their newly derived traits (adaptive advantages), early vertebrates established the fundamental way of life that their descendants have followed ever since. The telencephalon acquired, processed and stored information about the animal’s place in a world of chemicals and objects. It assessed the biological value of objects and places; and, crucially, it made choices about what actions to take or withhold. These early vertebrate ancestors needed to conserve energy, avoid risk and yet exploit opportunities for consuming nutritious items. (Risk Thermostat). In crude anthropomorphic terms, they were lazy and easily frightened, yet greedy. This combination obviously worked, but clearly they have a lot to answer for.

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Annex 1- Outdated Models Maclean appreciation Maclean published a similar theory that the origins of human brain structures can be found in our more primitive ancestors; (The Triune Brain), which became very popular (c.f. the “Chimp paradox”), except with the experts. He proposed that humans and other mammals, have a “reptilian brain”, which he identified with the basal ganglia, to go along with a “primitive mammalian brain” (roughly the limbic system) and an “advanced mammalian brain”- (the rest?).

Critics point out that many of the structures that Maclean identified as mammalian “advances”, such as the hippocampus and other components of the limbic system, originated much earlier. Mammals do not have “reptilian” structures inside their heads, although they do share homologues of many brain structures with other amniotes, including the basal ganglia. The cerebrum of stem amniotes includes the medial cortex and lateral cortex, homologues of the mammalian hippocampus and piriform cortex, respectively. These layers have a three layer allocortical structure, which differs from the mammalian six layer neocortex. The neocortex developed from the amniote dorsal cortex so was not entirely “new”! The reptilian dorsal cortex does have a homologue in the primary visual cortex of mammals. This part of the reptilian allocortex receives retinal inputs relayed via the Thalamus, just as the primary visual cortex does in mammals. The comparative evidence shows that the neocortex emerged during the evolution of mammals. So Maclean’s basic idea is not a hundred miles away from what is being argued here, and better than the prevailing view - just too simplistic and physiologically inexact for the professionals.

Homer Smith In a classic book “From Fish to Philosopher”, Smith recognises the fact that our ancestry includes not only the first philosophers, but also the first vertebrates. Although it may be wrong to say we retain an “inner fish” or a “reptilian brain”, it is true that a common ancestor gave rise to vertebrates, tetrapods, amniotes, mammals, primates and hominins – in addition to philosophers. 6 FRMBRNds0.1

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Annex 2 – Memory Terminology Representational Systems Evolution produced these systems as adaptations to address specific issues / challenges. People engaged in activities, are making use of a “representational system”; that is, they are using some internal representation of an “instantiation” of that particular situation. These representations can be visual, auditory, kinesthetic, or involve many other senses. In addition, a person creating a representation, is involving or recalling information (“MEMORY”), consciously or unconsciously. They may also be combining different types of memory, (episodic and semantic). Episodic memory is the memory of autobiographical events (times, places, associated emotions, and other contextual who, what, when, where, why knowledge) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred at a particular time and place. Semantic memory refers to general world knowledge that we have accumulated throughout our lives. Long-term memory is often divided into two further main types: 

Explicit (or declarative) memory and Implicit (or procedural) memory. (Declarative memory (“knowing what”) is memory of facts and events, and refers to those memories that can be consciously recalled (or "declared")). 

1. Explicit memory requires conscious thought—such as recalling who came to dinner last night or naming animals that live in the rainforest.  Explicit memory can again be divided into two categories: episodic memory, which stores specific personal experiences, and semantic memory, which stores factual information. 2. Implicit memory is the second of the two main types of long-term human memory. It is acquired and used unconsciously, and can affect thoughts and behaviours.  One of its most common forms is procedural memory, which helps people performing certain tasks without conscious awareness of these previous experiences.  Implicit memory is therefore sometimes referred to as unconscious memory or automatic memory.  Implicit memory thus uses past experiences to remember things without thinking about them. 

The (contribution?) performance of implicit memory is thus enabled (influenced?) by previous experiences, no matter how long ago those experiences occurred.

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Annex 3. Further thoughts So I still believe that the Tokyo insights were basically right, when we ”think”, there are a number of cognitive systems operating simultaneously in the brain, in a hierarchy that has evolved from primitive ancestors. So we are “conscious” of a dynamic, churning concatenation of complementary and conflicting, conscious and unconscious, stimuli from neural nets originating from external and internal sensors, mixed with prompts from memories and habits. At any instant in time this can arise from a variety of available (or persistent) contributions from the array of representational systems that have evolved to produce the human brain.

The Seven Systems? A. All organisms seem to have basic vital functions hardwired, to ensure appropriate responses to metabolic needs and external threats. The literature cites experimental measurement of these (very rapid) responses at the neuron level, which fit with the John Adams Risk Thermostat model. This level will have sensors and responses similar to the Grey’s Tortoise robot, designed to convey Avoid and Reward. Can we call this the Autonomic, or Adam brain system/ level (A) B. According to Murray, all vertebrates evolved a “Memory” function, which seems to have allowed reinforcement of repeated stimuli to be remembered (Pavlovian conditioning?). This informed the organism Better to avoid danger and Better to seek reward. (level / system B?). C. Again on Murray’s model, evolution of the Hippocampus structures added a memorised “Map” which on recall, or automatically, allowed knowledge of where to look, or to avoid (the Cartographic, Columbus or C level?). D. The Thalamus homologues seem to play a vital role in Dealing with conflicting or competing stimuli; and seems to Direct nerve signals to appropriate brain structures, rather like a Router in computing terms. (System / level D) E. Murray identifies another brain function that adds to the previous systems an ability to plan Explorations and Expeditions. (This foraging system we can denote as E?) F. & G. Again from Murray these must be the Feature and Goal Systems. H. This essentially Human system evolved to address the needs of a social being, but also according to Murray this Highest system, bestowed the ability to recognise oneself and other “selves” (System/ level H?)

Not Enough? I. I would add another newer system, which involves original, creative and overriding strategic thinking based on learned experiences. This level (I). I think therefore I am, could be thought of as the Philosopher system. But more importantly is needed if we take on Board Kahneman’s two systems (H&I?)

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