12

The Origin, History and Science of Memory
Neil Doherty

 Throughout human history, much of the 
brain and its functioning has been unknown. 
At first, the theory of mind was articulated by 
ancient Greek philosophers. Plato, for instance, 
declared that the Logistikon (interpretation 
of consciousness at the time) was, in fact, the 
thinking part of the soul. Aristotle subsequently 
proposed that the mind was an extension of the 
soul that involved knowing and understanding. 
Outside these two major contributions, not 
much else of the function of the human brain 
had been addressed, outside of its moral 
reasoning and decision making. Although the 
studies at the time had been primitive and 
informal, they did tackle many of the critical 
concepts about consciousness, will, and memory. 
However, memory seemed more tangential 
and was treated teleologically as a means of 
understanding consciousness. Up until the 20th 
century, very few people had questioned the 
extent, capacity, or mechanism of memory. It 
was lost in the deafening roar of debate over 
consciousness.
 However, in 1885,  the first account of 
memory as a function of crystallized intelligence 
had been proposed, with the advent of the 
famous Ebbinghaus curve from Ebbinghaus’ 
Über das Gedächtnis (Memory. A Contribution 
to Experimental Psychology, 2016). Though it 
seemed rather self-evident, the scientific data 
proving that memory decreased over time was 
revolutionary. As a direct result of Ebbingahus’ 
contribution, the study of human memory was 
thrust to the forefront of both psychology and 
early neuroscience. Eventually,   Richard Semon 
proposed in his 1904 The Mneme that memories 
created an engram, a seemingly permanent 
change in the physical structure of the brain 
that can be measured (12). Later in 1949, 
psychology researcher Donald Hebb developed 
Hebb’s Rule, the notion that memories were 
stored in connections between neurons known 
as synapses (65). This forms the basis of  our 
current understanding of memory, scientifically 
supported by the continued efforts of modern 
neuroscientists from the 1950’s onwards (most 
notably Dr. Karl Lashley, who in 1950 gave 
empirical evidence of engrams by eliciting 
episodic memories by electrically stimulating 
different parts of the brain with electrodes 
(Mastin, 2018). 

 Despite knowing about the nature of memory, 
there is little knowledge about what exactly 
constitutes memory, how it functions, and its 
relation to other cognitive processes. Currently, 
our understanding of memory is split between 
two interpretations of neural functioning: the 
modular approach and the holistic approach. The 
modular approach (first proposed by Jerry Fodor 
in 1983 when he published the book Modularity 
of Mind (2-5)) proposes that memories function 
differently in different parts of the brain as a 
result of a neural anatomical process known 
as functional specialization (neurons being 
functionally assigned different roles based upon 
localization and necessity (Wang, D. et al., 2014). 
To understand this approach, we must first 
understand how memories are formed. 
 Memories are formed by converting external 
stimuli into usable electrical signals. Touch, 
for example, uses unmyelinated dorsal root 
ganglia (DRG) neurons to detect pressure and 
proprioception (body orientation), allowing 
for afferent messages to be sent via the 
depolarization of action potentials -electrical 
signals created by electrochemical gradients 
(see figures 1.1 and 1.2 )(ch1_neuronv_biov2 
8-26)- once exteroreceptive (outer body) and/
or interoceptive (inner body) sensations have 
been detected. These messages then travel 
to the cortex via the gracilis muscle in the 
thigh, ascending up the spinal cord to the 
cunneatus, finally making their way to the 
second somatosensory cortex, which includes 
the amygdala and hippocampus (see figure 2.1). 
Proponents of modular theory then propose 
that memories enter the hippocampus from 
the Cerebral Cortex through the perforant 
pathway, which leads to the entorhinal cortex. 
This data then flows to the dentate gyrus where 
it is transferred to the pyramidal neurons of the 
CA3 region of the hippocampus, which sends the 
information to the axons of the CA1 region. The 
subiculum then relays the information back to 
the entorhinal cortex, which pushes out the data 
back into the cerebral cortex, where different 
memories are then divided to be encoded; 
repressed and emotionally episodic memories 
are sent to the amygdala and limbic system in 
people with PTSD or emotional trauma, while 
semantic memory is stored in the neocortex. 
Other information is mostly kept in the synapses 

between neurons via complex sequences of 
neurotransmitters stored in synaptic vesicles 
waiting to be released at depolarization into the 
synaptic cleft in both the hippocampus and the 
cerebral cortexes (see figure 3.1) (Rolls, E.T., 
1996).
 Holists suggest the very same anatomy, 

however they maintain that memories are stored 
across the entirety of the cortex, meaning that 
all areas overlap with little specialization in 
memory storage beyond the distinction between 
the storage of explicit (conscious) memories in 
the cerebrum and implicit procedural (muscle) 
and episodic memories in the cerebellum and 
amygdala (Ramachandran, 2009). In essence, 
holists posit that memory storage is almost 
completely indeterminate and generalized 
across the entire brain. Both seemingly contrary 
theories have significant experimental support, 
meaning the prevailing theory is that memory 
is a mixture of both holism and modularity. As 
a result, more recent focus has been given to 
understanding the cellular mechanisms to better 
delineate between the two systems to determine 
their roles in very destructive disorders like 
Alzheimer’s and PTSD.
 

Figure 1.1 Diagram of neuron

Figure 1.2: Image of the components of a synapse by which neurotransmitters are exchanged end signal transduction 
occurs.



13

 
 After addressing the physiological distinctions 
for approaching memory, it’s important to note 
that current studies on the procedure of recall 
have shown that memory has not been properly 
delineated from other cognitive processes as was 
originally thought. For instance, according to 
Tomita et al., functional Magnetic Resonance 
Imaging tests (fMRI) have determined that 
during voluntary recall, blood flow aggregation 
in regions of the frontal lobes associated with 
conscious thought increased, suggesting that 
feedback projections from prefrontal cortex to 
the posterior association cortex appear to serve 
the executive control of voluntary recall, not 
the previously believed sub-cortical regions 
responsible for unconscious activity. This 
implies that it is possible that memory and 
consciousness may not be separate at all. In 
addition, consciousness and memory have been 
discovered to emerge from the same cellular 
process. Memory is allegedly stored in complex 
sequences of pyramidal neurons that scientists 
now believe are capable of quantum computing 
by mechanism of tau protein synthesis in 
microtubules from ribosomes in the pyramidal 
neurons (orchestrated objective reduction 
theory or Orch-OR, also known as the Penrose-
Hammerhoff model). The specific make up of 
proteases, tau proteins, and Ubiquitin proteins 
forms a complex system by which signaling 
occurs to quantum level differences, in which 
electron transmission is specified to particle 
level accuracy. This is also now considered the 
main mechanism of consciousness, as such 
neurons also associate with other high gray 
matter areas of the prefrontal and cerebral 
cortexes. This makes the data stored infinitely 
complex due to the extensively minute degree of 
error and incredibly high intensity of specificity 
(Atmanspacher, H., 2004).  Though the Penrose-
Hammerhoff model is a relatively new projection 
that is still being tested for validity, it does 
provide a possible explanation for why non-
memory based conscious-driven parts of the 
cortex activate during voluntary recall. It should 
also be noted that the previously mentioned 
synaptic model for memory does imply that the 
synaptic cleft, which is associated with memory, 
is also responsible for signal transduction via 
neurotransmitters, indicating that there is some 
physiological correlation between the process of 
signal transduction and memory encoding and 
storage.
 An interesting advancement in our current 
understanding of the connection between 
memory and consciousness can also be found in 
stroke victims, specifically those that suffer from 
cerebral ischemia -brain damage caused by lack 
of blood flow to the brain- (Mayo Clinic, 2018)  
Patients who have such debilitating strokes have 
the potential to develop a condition known as 
Capgras Syndrome, a unique disorder affecting 

a person’s ability to relate memory to emotional 
experience. This rare disorder preserves the 
pathways for visual recognition within the 
posterior occipital lobe and temporal lobe, along 
with emotional centers of the brain such as the 
amygdala, parts of the diencephalon, and the 
basal ganglia. However, the connection between 
the two in the parietal lobe (now believed to 
be the fusiform gyrus) is damaged, producing 
an inability to share the processed information 
between the limbic system and the occipital lobe. 
As a result, the ailing patients are incapable of 
recognizing loved ones or processing emotional 
memories properly. Despite being able to 
recognize people of little significance in their 
lives and being able to experience emotion, these 
patients report being surrounded by impostors 
replacing their loved ones, hence the colloquial 
name “imposter syndrome”. (Ramachandran 
158-174) The problem, however, presents a 
surprising revelation: emotional memories are 
separable from conscious activity. In patients 
with Capgras Syndrome, there is a remarkable 
ability to consciously forget an individual 
within a short span of time; however, patients 
do exhibit an unconscious emotional response 
that is caused by an emotional “memory” of 
qualities of the individual. In other words, when 
someone with Capgras Syndrome catches up 
with an old friend, they fail to recognize the 
friend cognitively, however they unconsciously 
feel the typical emotions they would around said 
friend, indicating that emotional memory might 
be processed separately from conscious memory, 
only to interweave with consciously streamlined 
data in the fusiform gyrus. (Ramachandran, 
2009) Similarly, people with severe anterograde 
amnesia who are incapable of forming new 
crystallized memories are reportedly able to 
retain unconscious emotional memory storage, 
sometimes even exhibiting consistent behavior 
in spite of not understanding why or how they 
started the behavior (Sacks 23-43)
 Post Traumatic Stress Disorder, another 

debilitating neuropsychological condition, 
has revealed that the human brain is capable 
of altering its capacity of memory storage 
drastically. PTSD is a result of the overuse of 
corticotropin-releasing factor (CRF) in the 
hypothalamic-pituitary-adrenal axis system. 
In the brain, the thalamus circulates CRF to 
facilitate the release of adrenocorticotropic 
hormone (ACTH) from the pituitary gland, 
resulting in the adrenal gland releasing 
epinephrine. The epinephrine then operates in 
a negative feedback loop with norepinephrine 
by mechanism of auto-inhibition through 
presynaptic α2-adrenoceptors. This negative 

feedback loop prevents overproduction of 
cortisol and their consequent overstimulation 
of the pituitary gland, hypothalamus and 
hippocampus. (Bremner, J.D. et al., 1970)
 Normally, this noradrenergic response is used 
to maximize utility (more blood flow, more 
actin filaments prepared by ionized channels, 
more ready action potentials, and generally 
faster reflexes in physiological structures) in 
survival circumstances, increasing activity in 
the sympathetic nervous system in preparation 
for dealing with external threats. However, 
people with PTSD create CRF in extreme excess 
due to both genetic and epigenetic influences. 
Some people are born with more hypothalamic 
corticotropin-releasing factor mRNA, meaning 
more glucocorticoid protein synthesis occurs 
(Bremner, J.D. et al, 1970). Others can have 
previously unexpressed genes triggered by the 
environmental factors causing the use of more 
telomeres which are responsible for cortisol 
production (Yang, B.Z. et al., 2013).  This 
overabundance of CRF and cortisol has been 
shown to cause some impairment of intellectual 
ability in both crystallized and fluid intelligence. 
According to Dr. J. Douglas Bremner M.D et al., 
“Brain imaging studies have shown alterations 
in a circuit including medial prefrontal cortex 
(including anterior cingulate), hippocampus, 
and amygdala in PTSD… Stimulation of the 
noradrenergic system with yohimbine resulted in 
a failure of activation in dorsolateral prefrontal, 
temporal, parietal, and orbitofrontal cortex, and 
decreased function in the hippocampus.”
 Interestingly, these studies show that not only 
are memory and verbal ability reduced, but the 
very process of accessing memory is completely 
altered during triggered episodes. During post-
traumatic episodes, it seems that hippocampus 
activity is lower than normal while most 
brain activity is centered in the limbic system; 
specifically, the amygdala, posterior cingulate, 
gyrus, and parahippocampal gyrus are active 
in these periods. The reduced brain activity 
in areas associated with conscious memory 
retrieval explain the seemingly random and 
uncontrollable onset of traumatic episodes and 
most likely occur due to overstimulation of the 
sympathetic nervous system. In other words, the 
mechanism of PTSD is most likely related to an 
overstimulated fight-or-flight system exercising 
dominance over the less developed cognitive 
system of the brain. The dominance occurs due 
to the limbic system being a far more responsive 
and developed brain structure, one that operates 
on hormonal messaging that is longer lasting 
than simple synaptic signaling. PTSD thus shows 
that memories are in fact not entirely voluntary 
and occur due to several diverging mechanisms 
rather than one (Bremner, J.D. et al., 1970).
 To summarize, memory has been a relatively 
uninvestigated subject. However, with the advent 
of modern neuroscience and growing prevalence 
of memory disorders, it has become a scientific 
phenomenon worth investigating. Memory has 
been linked to many phenomena, branching 
emotion, consciousness, instinct, and genetics 
in a melting pot of complex neural functioning. 
Memory may well be the key to understanding 
the connection between mind and matter, 
consciousness, intelligence and human emotion.

Figure 2.1: Image of the path by which sensory information is sent

Figure 3.1: diagram of the hippocampus and position in the brain



14

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