# Logic and Math

So here we have a brain whose association cortex works overtime to combine sensory information into a stream of relationships in space and time. In fact, you cannot shut off this process or stop the brain from constantly searching its sensory inputs for patterns, even when there are no patterns to be found!

The time domain is particularly interesting because it is here that we build up the ideas of cause-and-effect and create various rules-of-thumb that help us predict the future, find food, and many other activities. This specific rule-type association largely takes place in the dominant hemisphere of the brain (left side for right-handed people) which also has the speech center. Specifically, the frontal lobes are generally considered to be the logic and reasoning centers of the brain. So when the brain is talking to you, it also has easy access to logical tools of thinking. We also have a minor hemisphere (right-side for right-handed people) that specializes in pattern recognition, but it contains no language centers and is therefore mute. Its insights about the patterns that it finds in sensory data are totally overtaken by the constantly babbling left-hemisphere. All it can muster is that non-verbal feeling of ‘Eureka!’ you get  once in a while.

This sequence of brain scans shows the four stages of math problem solving from left to right: encoding (downloading), planning (strategizing), solving (performing the math), and responding (typing out an answer).

Anyway, brain researchers have done brain imaging studies to explore where math reasoning occurs. They found that, when mathematicians think about advanced concepts, the prefrontal, parietal, and inferior temporal regions of the brain become very active. But this activity didn’t also happen in brain regions linked to words. This means, as many mathematicians can tell you, mathematics is not related to the brain’s language centers. It is an entirely different way of communication. In other words, you can carry-out mathematical thinking without an internal voice speaking. It is an entirely non-verbal activity until you are interested in communicating your results to someone else. I know this myself when I am solving complex equations. Not a single conscious word is involved. Instead, I move my hands, squirm in my chair, and robotically step through the methods of solving the equations without any verbal prattle like ‘Ok…this goes over here and that goes down here and x moves to the other side of the equals sign’ …and so on. I keep telling the public that math is the language of science, but in fact it is not really a language at all. It’s like saying that oil is the language of painting a work of art! In fact, when you are proficient at mathematics, you are behaving like a concert violinist who does not think about each note she plays, but flows along on a trained sequence of steps that she learned. Her sequence of fine motor skills are stored in the cerebellum, but a mathematician’s skills are stored in an entirely different part of the brain.

Researchers have found a group of a few million cells located in a region called the inferior temporal gyrus. These cells seem to respond very strongly when you are doing concrete, numerical calculations like balancing your bank account, filling out your taxes, or plugging-in numbers in a complex equation to get an answer . So the brain does have discrete regions and clumps of neutrons that make mathematical reasoning possible. An entire hemisphere is dedicated to ‘logical analysis’, but specific locations allow you to work with this implicit logic in an entirely symbolic manner that resembles the language centers in the Broca’s and Wernicke areas, which facilitate speech and writing words.

So here we now have all the elements for creating a model of the outside world by using sensory data to find patterns in time, and to use these patterns to eventually deduce general mathematical If A then B logical statements about them that are entirely symbolic, and far more accurate than what the brain’s language centers can provide through its endless chatter.

The basis for all these deductions about the world outside the brain is a concrete understanding of what space and time are all about. We learn about space through our binocular vision, but also because our mobility allows us to move through space. Even with perfect stereo vision, you have no idea what those objects are that you are looking at unless you can literally walk over to them and appreciate their actual sizes, textures and other features. So our deep, personal understanding of 3-dimensional space comes about because we have mobility and stereo vision. But actual vision as a sense may not be that important after all. Echolocation used by bats and dolphins is not a visual decomposition of the world but an auditory one, processed to give back a 3-dimensional model of the world without vision, color or even the perception of black and white being involved.

Evidence from  brain-imaging experiments indicates that, when blind people read Braille using touch, the sensory data is being sent to, and processed in, the visual cortex. Using touch, they get a sense of space and the relative locations of the raised dots that form Braille letters . Although the information is processed in the visual cortex, their impression is not a visual,  but is instead a directly spatial one without the intermediary of vision to get them there!

Next time I will begin the discussion about how astronomers and physicists ‘envision’ space itself.

Check back here on Monday, December 12 for the next installment!

Mathematical Ability Revealed in Brain Scans, 2016, By Mindy Weisberger
http://www.livescience.com/54370-math-brain-network-discovered.html

Other related essays:

How Do Blind People Picture Reality? By Natalie Wolchover
http://www.livescience.com/23709-blind-people-picture-reality.html

# Rules-of-thumb

There are at least two basic ways that we create associations. The first is associations in space. The second is associations in time.

Associations in space include recognizing static objects like chairs, trees, cars and people. The reason this works so well is that we live in a world filled with many different kinds of more-or-less fixed objects so that two or more people can agree they have similar attributes.

Associations in time include musical tunes and sounds, or associating one thing (cause) with another thing in the future (effect). For many of these dynamic associations like music, two people with normal hearing senses hear the same sequence of notes in time and can agree that what they heard was a portion of a familiar song, which they may independently be able to name if they have heard it before and made the appropriate associations in memory. But your exact associations related to the song will be different than mine because I associate songs with episodes in my life that you do not also share. Remember, the brain tags everything with patterns of associations unique to the individual.

The human brain is adept at pattern recognition. It can dissect its sensory information and see patterns in space and time that it can then associate with abstract categories such as a chair or a bird, and even specific sub-categories of these if it has been adequately trained (at school, or by reading a book on ornithology!). An upside-down chair seen in the remote distance is recognized as a chair no matter what its orientation in the visual field. A garbled song heard on an iPhone in a loud concert hall, or a particular conversation between two people in a noisy crowd, can also be detected as a pattern in time and recognized. The figure shows some of the brain connection pathways identified in the Human Connectome Project that help to interpret sensory data as patterns in space and time.

Patterns in space let us recognize the many different kinds of objects that fill our world. In the association cortex, once these identifications have been made, they are also sent on to the language centers where they are tagged with words that can be spoken or read. Once this step happens, two individuals can have a meaningful conversation about the world beyond their bodies that the senses can detect. Of course when both people say they have a specific category of objects called Siamese cats, they are most certainly associating that name with slightly different set of events and qualities corresponding to their cat’s personalities , fur patterns, etc..

The next step is even more interesting.

Just as the brain generalizes a collection of associations in space to define the concept of ‘cat’, it can detect patterns in time in the outside world and begin to see how one event leads to another as a rule-of-thumb or a law of nature. If I drop a stone off a tall cliff, it will fall downwards to the valley below. If the sun rises and sets today, it will do so again tomorrow. There are many such patterns of events in time that reoccur with such regularity that they form their own category-in-time much as ‘cat’ and ‘chair’ did in the space context. ‘If I visit a waterhole with lots of animals, there is a good chance that tigers or lions may also be present’. More recently, ‘If I stick my finger in an unprotected electrical outlet, I will probably be electrocuted!’. This perception of relationships is one of cause-and-effect. It has been studied by neurophysiologists, and is due to stimulation of part of the cerebellum and the right hippocampus. These brain regions are both involved with processing durations in time.

Over the centuries and millennia, the patterns in time we have been able to discern about the outside world have become so numerous  we have to write them down in books, and also put our children through longer and longer training periods to master them. This also tells us something very basic about our world.

Instead of being a random collection of events, our physical world contains a basic collection of rules that follow a ‘logical’ If A happens then B happens pattern in time. Physicists call these relationships ‘laws’ and their particular patterns in time and space can be discerned from measurements and observations made of phenomena in the world outside our brains. The brain can also work with these laws symbolically and logically, not by describing them through the usual language centers of the brain, but through a parallel set of centers that make us adept at mathematical reasoning.

In my next blog, I will discuss how mathematics and logic are intertwined and help us think symbolically about our world.

Check back here on Friday, December 9 for the next installment!

Space, Time, and Causality in the Human Brain
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4008651/

# What the…!!!!

You would think that a scientist lives in a purely rational world, but sometimes even we fall victim to events that are hard to explain at the moment. Here are my two favorite, and involuntary, journeys into the world of altered states!

I have had three experiences that some sufferers of migraine headaches may know all too well. Suddenly from out of nowhere, you may see flashing or shimmering lights, zigzagging lines, or stars. Some people even describe psychedelic images. For me, each one came on suddenly and caused me a bit of consternation before I figured out what was going on!

Each time, I saw a jagged crescent-shaped light that drifted across my visual field. I did not have a migraine headache either before or after, since I do not suffer from these painful conditions. But the shape and behavior of the image was identical to such migraine auras.

Called scintillating scotomas by opthamologists, in my case the effect occurred in the same part of my visual field no matter where I moved my eyes, so I knew that something was going on way up in my brain to cause it, and not in my retinas, like the experience of having those pesky ‘floaters’. Instead, it is caused by what is termed a ‘cortical spreading depression’. This is literally a physical wave of hyperstimulation followed by neural inhibition, that spreads out from the visual cortex and into the surrounding association areas at a speed of about 5 millimeters per minute. The whole thing lasts less 60 minutes and is quite amazing and slightly painful to watch. If you are driving a car at the time, it is extremely distracting and even dangerous. My events began as a flickering spot that expanded into a nearly ring-like, zig-zag shape about half the size of my visual field before fading away.

https://en.wikipedia.org/wiki/Scintillating_scotoma

The second perceptual event that I have never forgotten was much more complex.

I woke up in the semi-darkness of my bedroom and could see the dim shapes of the furniture around me, but I absolutely could not move so much as an eyelash. My eyes were open, but felt like they were very dry and begging for me to blink to get some tears going to reduce the irritation. But that was not the thing that captured my attention. There, floating at arms-length was a bright visual scene about as big as a dinner plate that had a horse running around in a corral. As I watched, the initially very clear image became less and less distinct until it faded out completely. Within a few minutes, sounds began to flood back and I could again move around in a fully awake state.

I had this experience in my early-50s and it was never to reoccur. Now, I have had quite a few waking dreams in my life, where I woke up in a dream realizing where I was, then waking up a second time to the real world, but this was a completely different experience.I have searched the literature to look for an explanation, and come across discussions of waking dreams and lucid dreaming, but this event seems to be different. Unlike a lucid dream, I was not aware that I was dreaming as I was watching the visual scenery of the horse in the corral. Instead it did not seem like an unusual experience at all. My tendency towards scientifically analyzing my experiences did not kick-in. All I could do was watch and marvel at the event with a feeling of awe, and definitely not fear.The nearest I could find to my experience is the ‘Type 2 false awakening’ where ‘The subject appears to wake up in a realistic manner, but to an atmosphere of suspense.[…] The dreamers surroundings may at first appear normal, and they may gradually become aware of something uncanny in the atmosphere, and perhaps of unwanted [unusual] sounds and movements.’

There is also the phenomenon of sleep paralysis ‘in which an individual briefly experiences an inability to move, speak, or react. It is often accompanied by terrifying hallucinations to which one is unable to react due to paralysis, and physical experiences. These hallucinations often involve a person or supernatural creature suffocating or terrifying the individual, accompanied by a feeling of pressure on one’s chest and difficulty breathing.’

Well, there was nothing terrifying about my experience. In fact, it was extremely pleasurable and awe-inspiring!

In reflecting back on these events, I find myself delighted that I experienced them because sometimes you want to have experiences in life that are extremely unusual and hard to explain just to have something to think about other than the predictable day-to-day world. I’m sure there are detailed medical reasons for each of my apparitions, because they all are related to how my brain works. Our brains are amazing organs that work overtime to make sense of the world, but they are still fallible.The difference between passing a kidney stone and a minor hiccup in the brain, is that our kidneys are not conscious. But, any little innocent tweak to our brain physiology is immediately interpreted as a change in behavior or of our conscious experience of the world.

So the next time you experience something ‘odd’, don’t be too worried about it. Just sit back and try to enjoy the altered experience. In the end, it may only be a completely innocent, though inscrutable, brain hiccup!

In my next blog I will describe how a brain filled with complex associations manages to make sense of it all!

Check back here on Wednesday, December 7 for the next installment!

Ocular migraines:
http://www.healthline.com/health/causes-of-ocular-migraines#Overview1

False awakening:
https://en.wikipedia.org/wiki/False_awakening

Sleep paralysis:
https://en.wikipedia.org/wiki/Sleep_paralysis

# What does it mean?

What happens to all this sensory information that gives you a concrete idea about the things that exist in your world?

We saw how the flow of sensory information at any one time is enormous. It starts out as separate streams of information that flow to specific brain regions as their first stop, but then after that the information radiates to many different regions in the brain where it gets mixed with our emotions, and even with other sensory information. This is a process that is called association, and a large volume of the brain is called the Association Cortex for that reason.

At first the auditory information called purring, is connected to other sensory information occurring at the same time, for instance, the feeling that something furry is brushing against your leg. These two pieces of information become associated with each other, especially if they are connected to a similar combination you experienced earlier, and which was associated in your language cortex as the sound of the word ‘cat’ or the written word ‘cat’. Communicating this information is then handled by Broca’s Area (speech generation ) and Wernicke’s Area (speech comprehension).

The brain creates meaning by associating sensory information with specific categories of past experience. Nothing can really be understood except through a complex process of being associated with other things you have experienced, or learned. It’s like some enormous, interlinked tapestry of connections, and adding a new bit of information is always about fitting it into what has already been experienced in some way. But if that were all that there is, we would simply be walking encyclopedias.

Most of us have senses that are pretty well-defined. For example, the optic nerve transmits what each eye’s retinas detect and passes this on to the visual cortex at the back of the head after some of this information is first linked by neurons to a small brain region called the suprachiasmatic nucleus and then on to the pineal gland (to detect the day-night cycle). It also connects with the thalamus where it gets associated with other sensory stimuli. The three types of retinal cone cells are tuned to slightly different wavelengths of light and send the usual neural signals along the optic nerve. The outside world actually has no color at all. Everything is decided by the wavelength of light, and this number does not include color information. But by the time the visual cortex and its related association cortex is finished processing the information from the cones, you have a definite internal sense of color being an intimate part of the world. This is, however, very different than seeing the world in black and white, which is actually a better representation of what the world looks like. Our retina also have rod cells that are very sensitive to light intensity at all visual wavelengths, but give you only a sense of a grey world!

By coding light frequency information as well as intensity, our eyes and brains over eons of evolution have ‘decided’ that this extra color information has survival value. It can help classify things in terms of specific frequency fingerprints. For example, a coral snake is deadly and a scarlet king snake is harmless. Their skins have yellow and red bands, and the rhyme ‘Red touch yellow, kills a fellow but red touch black is a friend of Jack’ helps you distinguish between the two. You would be dead if all you could see is black and white. In fact, the complex color selections seen in nature have actually co-evolved with color vision over millions of years. The scarlet king snake adapted a version of the color coding used by coral snakes to fool predators into thinking it was a poisonous snake!

Sometimes this process can be flawed. We all know about color blindness, which affects about 8% of men and 0.5% of women. This happens when one of the three cone cell populations in the retina do not work properly. There is no way for the brain to correct for this because the retina has eliminated an important color sense long before the information reaches the optic nerve and the visual cortex.
There is another sensory malady that is even more unusual. Called synesthesia, it is caused by synaptic connections between otherwise separate sensory channels. For instance, you might see letters of the alphabet as having distinct colors on the page, or associate a specific sound with a color, among dozens of other documented possibilities. It is actually much more common than you might suspect. Have you ever felt that numbers have a definite location in space, or that 1980 is ‘farther away’ than 1990? Studies of the brain show that these mixings happen because of cross-wiring of neurons in the brain, either due to genetics or due to training when you were very young.

So, it isn’t even true that everyone perceives the outside world in identical manners. This leads to differences in how each person categorizes events and their internal associations with other things we have experienced. So with all of these variations in exactly what a ‘cat’ is, how do we create models of the world that let us function and survive without having accidents and getting killed all the time?

In my next blog I will describe two very unusual, personal experiences that show how our experience of the world can be temporarily distorted.

Check back here on Monday, December 5 for the next installment!
Seeing Color: http://www.webexhibits.org/causesofcolor/1C.html

# A Stroke of Insight

Once the firehose of sensory information reaches the brain, a bewildering process of making sense of this data begins. The objective is to create an accurate internal model of the world that you can base your next decisions upon. To do this, all of the many bits of data flowing along the sensory neurons have to be knitted together somehow. Thanks to the unfortunate circumstances of minor strokes, brain researchers have been able to track down many of the important steps in this information processing.

You might have heard of the experiences of limb amputees who, for a time, experience the ‘phantom limb’ effect. The neurons having been severed still report back to the brain that their stimulation means the limb still exists, and for a period of time the amputee has to deal with the ghost limb that is not really there. In another bizarre situation, a stroke victim has a perfect understanding that their left arm belongs to them, but insists that their right arm belongs to a relative living 1000 miles away. This malady is called asomatognosia by neurophysiologists.

From many studies of how pinpoint strokes affect brain function, neuroanatomists have identified specific regions of the brain that allow us to integrate our sensory information and create a coherent model of the outside world as it exists in space and time. The first thing the brain has to do is to have a ‘sense’ of its own body and how it is located in space. It also has to identify this ‘self’ as being different from that of other people. If it cannot do this accurately, it cannot decide how to move in space, anticipate the consequences of that movement, or how to anticipate and empathize with the actions of other people. Nearly all of this activity seems to be relegated to a single area in the brain.

The temporoparietal junction (TPJ) takes information from the limbic system (emotional state) and the thalamus (memory) and combines it with information from the visual, hearing and internal body sensory systems to create an integrated internal model of where your body is located in space. The TPJ has left and right ‘lobes’ that control your ability to pay attention (right) and to anticipate other people’s emotions and desires (left). Patients with schizophrenia have abnormal levels of stimulation in the TPJ and cannot discern the intentions of other people. Stimulation of the right TPJ by placing electrodes in unesthetized patients leads to out-of-body experiences, schizophrenic behavior, and the phantom limb effect. The right TPJ tries to create a coherent body image from many different, and sometimes contradictory sensory inputs. When this process breaks down because the contradictory information is too strong to inhibit or ignore, you experience that you actually have two distinct bodies in space. This seems to be the direct, neural basis for out-of-body experiences.

But there is an even stranger brain region whose stimulation leads to an error in deciding where the body and self ends in space, and where the outside world begins.

The posterior cingulate body plays a huge role in self-location and body ownership. What this means is that we experience our body as having a definite location in space, and that this location is where you, the ‘Self’ is located. Strokes in this region cause asomatognosia patients not to recognize a limb as belonging to them. But you don’t have to be a stroke victim to experience this dislocation of body and self.

If you sit at a table facing a barrier that lets you see an artificial, life like right hand but not your real right hand, and you rhythmically stroke the real hand, eventually your brain gets fooled into believing that the artificial right hand is actually yours. If someone suddenly stabs the artificial hand, you will actually jump reflexively as though, for just an instant, the brain got confused about which was your real right hand being attacked!

The Posterior Superior Parietal Lobule gives us a sense of the boundary between our physical body and the rest of the world. When activity in this brain region is reduced, the individual seems to lose a sense of where their body ends and the rest of the world begins. The feeling is one of having ‘merged with the universe’ and your body is in some way infinite. Mindfulness practices such as meditation can modify the stimulation of this region and give the practitioner exactly this dramatic experience.

So you see, once sensory data gets to the brain, it is in for an amazing ride through many brain regions that help us build up the person or self that we feel we are through space and time.

By the way, for a fascinating introduction to these topics, read V.S. Ramachandran and Sandra Blakeslee’s book ‘Phantoms in the Brain: Probing the mysteries of the human mind’

Here is an interesting 2013 research paper in the journal Frontiers in Psychology ‘Alterations in the sense of time, space, and body in the mindfulness-trained brain: a neurophenomenologically-guided MEG study’ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3847819/

The connection between meditation and brain region function and stimulation is covered in this article: Mindfulness Practices and Meditation. https://neurowiki2012.wikispaces.com/Mindfulness+Practices+and+Meditation

But now let’s consider how the brain actually makes its models.

Check back here on Friday, December 2 for the next installment!

# Making Sense of the Senses!

If you are trying to understand the world beyond your body, it’s probably a good idea to also understand just how your observations are being made and then interpreted. Our brains process a lot of sensory information, but interpreting it is a lot more fluid and fallible than you might believe!

First of all, there is no ‘person’ inside your head looking through a TV screen into the outside world through your eyes.

Sensory information is received in small bits of impulses traveling along neurons. A visual scene dissolves into clusters of rod and cone cells in the retina that sense edges, colors, and other elemental features of what you are looking at. These qualities are not stored in the visual cortex adjacent to each other like pixels in a picture, but grouped together by thematic features. It is only at the next level of neural connections (called synapses) that associations between areas in the visual cortex are made in order to identify archetypical objects such as cars, houses and, yes, grandmothers! These neurons also make many different synaptic connections along the way to help process the information flow long before you perceive it as an integrated whole. This figure shows, for example, a few of the neural pathways that connect the visual cortex regions ( V1, V2, V3) all the way to the prefrontal cortex (PF).

What you see is sometimes not always what you get. Your neural networks may actually remove information from your conscious perception of the world. A frog’s retinas only pass information to its brain when something is moving in the visual field. Its brain doesn’t even GET the basic information that things like perfectly edible flies are standing still on a nearby leaf! Only when they move does the retina communicate to the frog’s brain that there is a fly ‘out there’ to go after and eat. You know that ‘blind spot’ in your eye? The brain fills it in with fabricated information so that you do not see a black spot the size of a quarter at arms-length. Our brain is actually lying to our conscious perception of the world!

Second of all, many of the neurons at the lowest level make connections to the limbic system and are ‘tagged’ with many different emotional states .

The most important of these taggings being the self-preservation, fight-or-flight response. For example, there is very high survival value to quickly tagging a distant shadow as either a predator or a non-predator. Not all shadows will be a lion, but in the grand scheme of evolution even a rule-of-thumb that works only 10% of the time can mean the difference between vital genes being passed on to the next generation or not. This identification has to be made very quickly before you have time to logically consider all the non-threatening possibilities for what the shadow might actually be.

This tendency towards making snap decisions that over-ride time-consuming reasoning has high survival value and is hard-wired into our brains, but it also screws things up as we apply the same data to rationally understanding the world around us. The best case of this is in the eyewitness reporting of crimes. Eyewitnesses are almost always in a highly-emotional state, and great care has to be taken in the courtroom to compare accounts and distill from them the actual facts. Sometimes eyewitness accounts have to be thrown out entirely.

Another big problem with the brain is that it has a nasty habit of using the same neural circuits to handle different tasks. This leads to some extremely crazy situations.

We all like to visually imagine ourselves in different situations as we day dream, read a good novel, or are fast asleep in bed. These visual images and other imagined relationships often use the same circuitry needed for carefully examining the outside world and making sense of it. What this means is that there is actually a neural connection between our imagined world and the hard-rock world we live in. Most people can easily distinguish the difference, but sometimes our imagination, dosed with the limbic system’s associations, can confuse what we are actually seeing or experiencing, not based on an actual experience, but based instead on an imagined one. You can actually improve some elements of sports performance by internally visualizing in detail the actions you want to perform. It seems that imagined activity can train the cerebellum almost as well as the actual act!

Our brain and sensorium have to work together to identify patterns that help us survive, or at least not get injured too badly. There can be some sloppiness in this process that allows a few people to misunderstand gravity and walk out a 35th floor window, but we have evolved so that this is a very rare occurrence. But still, there are many ways in which human perceptions can be misinterpreted or even distorted by the brain as it tries to process billions of bits of information every second against a wash of emotions and other states-of-mind.

In the next blog, I will describe how strokes have helped neuroscientists understand how human brains create consistent models of the world, and how this process can break down with some rather unbelievable results!

Check back here on Sunday, November 27 for the next installment!

# Making Sense of the World

Ask just about anyone how many senses a normal human has and the immediate answer will be five: sight, hearing, taste, smell and touch. By the way, I always manage to forget that last one for some reason!

The oldest mention of this particular list goes all the way back to the Hindu Katha Upanashad written in the 6th century BCE. Even Shakespeare mentions them as the ‘five wits’ in King Lear! But a lot has happened since way back when. The entire idea of ‘scientific research’ came into its own, and now there are a whole lot of other human senses that have been added to the classical mix we learn in grade school.

Sense Number Six: You can detect heat and the temperature of any object you touch or are placed close to. Your skin has thousands of little ‘receptors’ that individually detect the attributes of cold and warm.

Sense Number Seven: You can detect whether you are standing upright or lying down through the balance receptors in your inner ear, which are hollow loops filled with liquid. The movement of this liquid in each loop is sensed by neurons and tells the brain your head’s position in 3-dimensions.

Sense Number Eight: Pain is a sense that is not just the overloading of touch or pressure receptors in the skin. In fact we have three different groups of pain receptors that signal internal organ damage, external skin damage, or damage to our bones and joints.

Sense Number Nine: Another overlooked sense is proprioception: the ability for you to sense the orientation of your body and limbs in 3-dimensional space. Without this very important sense, you would not be able to walk, jump, dance, type at your keyboard, or a thousand other activities that make up your life.

Sense Number Ten: Chemoreception is the ability of your body to detect changes in the foods you eat, and signal the body to reject that food if it fails to pass certain internal tests. This sense can cause your stomach to contract, cause you to vomit, and cause changes in your vascular system,: ‘OMG I just ate rotten fish!’

Sense Number Eleven: Although not a specific cellular feature of the nervous system, every normal human has a perception of their place in time. Part of this is our 24-hour circadian rhythm, but through brain activity, we have a timing sense that allows us to sing, dance and play a musical instrument correctly. It also helps us locate ourselves in the present moment within our accumulated memories.

Sense Number Twelve: Outside versus inside. We have a unique sense of where our body ends and where the outside world begins. Without this, we would identify every sensory stimulus as originating within our body, and that our body has grown to encompass the entire physical world ‘outside’. More on this later!

Sense Number Thirteen: Friend versus Foe. Our cells have proteins on their surfaces that identify to our immune systems whether a cell is part of our own body, or is a foreign interloper.

If you think this range of senses covers all of the biological possibilities, there are many more senses that some animals have, and perhaps we also do at some very, very low level.

Sharks and some other fish can detect electrical fields with specialized receptors in their skin. Many animals can detect earth’s magnetic field and use this to navigate. Bees can detect polarized light, which they also use for navigation. The vomeronasal sense allows animals to detect the pheromones of other members of their species and use this to identify a mate in estrus, or members of their own clan. Plants can directly sense gravity and use this to help them grow upwards. Both animals and plants can detect slight changes in air moisture to precisely identify where a source of water is located.

The earliest known senses were developed by single cells to detect changes in various chemical concentrations in water – a potential food source. But by far the oldest sense among complicated organisms is vision. This particular sensory skill has been re-invented literally hundreds of times by evolution across millions of different organisms.

So there you have it. Senses are a brain’s way of detecting an organism’s place and situation in the physical world. Amazingly enough, human brains do not take-in all of the information generated by our senses. If it did, we would be in a near-constant state of epilepsy! So what our brains do is to actively suppress most of the sensory information our receptors generate before it even reaches our consciousness. In fact, if you were to look at the neural activity of the brain, far more neurons are devoted to the brain talking to itself, than checking on what’s happening in the outside world!

So what does the brain do with all of this information?

That will be the topic of my next blog!

Check back here on Friday, November 25 for the next installment!