Frozen in time

Our memories are thoughts and experiences frozen in time for later use. Organisms evolved their ability to preserve past experiences, especially those related to reward/punishment outputs, because this offered them an advantage in surviving and reproducing.

There are patients whose focal epileptic crises located in the hippocampus manifests through a panoramic view of one’s life during the crisis; although the hippocampus is also the main location responsible for Alzheimer”s symptoms, it is not the only place in our brain that stores data.

The hippocampus. From Wikipedia

The human memory can be:

I. declarative/explicit

– it allows us to preserve facts and events

– it is located in the hippocampus, the medial part of the temporal lobe, the diencephalon

II. non-declarative/procedural/implicit – it preserves “how to/algorithms”

– behavioral (abilities, customs) – located in the striatus, motor cortex, cerebellum

– identification/detection – located in the neocortex

– basic associative learning: emotional outputs (located in the limbic system) and muscular outputs (located in the cerebellum)

– non-associative learning – located in the reflex arcs

What is the importance of all these, you may ask? Memories are what define us in the end.The human memory is not reliable like that of a computer, but it still represents a continuum between our different stages in time.

As technology advances, so does our definition of death. A patient that is intubated and has a heart pacemaker – so can’t breathe  nor maintain a heart beat on its own- can’t be legally declared dead unless one’s own brain is dead. This is equaled to total irreversible cerebral ischemia.

Yet we know that we temporarily lose our consciousness during sleep every night – not to mention anesthesia or hypothermia – and yet we preserve our personal identity because our memories are still there.

This is how a new definition of death appeared – the information-theoretical death:

“A person is dead according to the information-theoretic criterion if their memories, personality, hopes, dreams, etc. have been destroyed in the information-theoretic sense. That is, if the structures in the brain that encode memory and personality have been so disrupted that it is no longer possible in principle to restore them to an appropriate functional state, then the person is dead. If the structures that encode memory and personality are sufficiently intact that inference of the memory and personality are feasible in principle, and therefore restoration to an appropriate functional state is likewise feasible in principle, then the person is not dead.”

(Ralph Merkle, Molecular Repair of the Brain)

This definition is still not accepted legally today but it can be in the future.

For the moment, we can’t transfer but pieces of our memories to other data storing devices – we can do this by writing, photography, sound or video recording onto stones/papyrus/paper/computers and by talking influencing others’ behavior; yet no human being can “download” one’s whole mind at a certain moment and neither can one “upload” it back or to a different hardware.

The difference between the same piece of information located in a book and in one’s brain is that the biological hardware can use this information (which is a different process than the simple retrieval of data) as it has consciousness. Unless we will find a replacement for the neuron programmed to decay, our knowledge and lives will be limited by the cerebral definition of death.

Have we been looking for consciousness in the wrong place?

Consciousness equals awareness of self and of the exterior environment. While studying neurology, I learnt about the Glasgow Coma Scale to identify consciousness states by measuring 3 outputs:

– the verbal response

– the eye response

– the motor response

The neural doctrine prevails in the mainstream literature , but some articles in the Journal of Consciousness Studies by Johnjoe McFadden made me think whether we have been looking in the wrong place for the neural correlates of consciousness.

While the neural doctrine asserts the neural synapses as the physical storage of memory and information transmission being made with the help of action potentials and chemical neurotransmitters, it does not identify the physical equivalent of consciousness. The electromagnetic field theories of consciousness identify the brain’s endogenous electromagnetic field as the substrate of consciousness.

An electromagnetic field is produced by electrically charged objects and can be described by the Maxwell’s equations :

and by the Lorentz force law:

In Seven Clues to the Origin of Consciousness, Johnjoe McFadden identified these clues to the origin of consciousness:

Clue 1: Consciousness generates phenomena in the world. It is a cause of effects.

Clue 2: Consciousness is a property of living (human) brains. As far as we know, it is not a property of any other structure.

Clue 3: Brain activity can be conscious or unconscious.

Clue 4: The unconscious mind can perform parallel computations but conscious appears to be serial.

Clue 5: Learning and memory require consciousness but recall may be unconscious.

Clue 6: Information that is encoded by widely distributed neurons in our brain is somehow bound together to form unified conscious percepts.

Clue 7: Consciousness and awareness are associated not with neural firing per se but with neurons that fire in synchrony.

The main arguments for this specific theory – the cemi theory- are:

– the relationship between firing synchrony of neurons and consciousness

– the research techniques that influence the nervous system or identify its endogenous electromagnetic field with the help of static charges or dynamic charges (currents).

These include:

– transcranial direct current stimulation

– transcranial alternating current stimulation

– transcranial magnetic stimulation

with their cranial equivalents and:

– electroencephalography

– electrocorticography which is intracranial EEG

– magnetoencephalography

When I first read about this theory I thought it is very suitable to experiments. Indeed the author makes a series of testable predictions detailed in cemi_theory_paper from which I quote:

(1) Stimuli that reach conscious awareness will be associated with em field
modulations that are strong enough to directly influence the firing of motor
neurones.
(2) Stimuli that do not reach conscious awareness will not be associated with em
field modulations that affect motor neurone firing.
(3) The cemi field theory claims that consciousness represents a stream of infor-
mation passing through the brain’s em field. Increased complexity of con-
scious thinking should therefore correlate with increased complexity of the
brain’s em field.
(4) Agents that disrupt the interaction between the brain’s em field and neurones
will induce unconsciousness.
(5) Arousal and alertness will correlate with conditions in which em field fluctu-
ations are most likely to influence neurone firing; conversely, low arousal
and unconsciousness will correlate with conditions when em fields are least
likely to influence neurone firing.
(6) The brain’s em field should be relatively insulated to perturbation from
exogenous em fields encountered in normal environments.
(7) The evolution of consciousness in animals should correlate with an increas-
ing level of electrical coupling between the brain’s endogenous em field and
(receiver) neurone firing.
(8) Consciousness should demonstrate field-level dynamics.

In the end, these 2 videos present an intracranial EEG after right frontal craniotomy and a transcranial magnetic stimulation.

Mathematical models in neuroscience

Mathematical models are mandatory for designing neural prostheses that can close the nervous circuit in order to treat a neurological disorder. Here are some sites that shared their mathematical models for the rest of us in order to use and improve them!

SenseLab – This is a project funded by The Human Brain Project and it includes these databases:

– neuronal databases: CellPropDB, NeuronDB, ModelDB,  MicrocircuitDB

– olfactory databases: ORDB, OdorDB, OdorMapDB

– disease databases: BrainPharm

If you need a mathematical model of a certain brain region, here is a very useful list.

In order to run these models, I advise you to download the NEURON software. In order to learn how to use it, here is an online version of exercises from the 2008 summer course.

Visiome is a database where you can find a lot of mathamatical models related to vision.

CellML is being developed by the Auckland Bioengineering Institute at the University of Auckland.

A free software to open the CellML files is Cellular Open Resource .

BioModels Database is a database of mathematical models of biological interest.

If you know of any good database of such mathematical models, please leave a comment!