The book is an insightful journey into the contemporary understanding of the human brain and how scientists are trying to replicate it. Major takeaways from the book are listed below.

Thought experiments in the world

1. Charles Lyell was the first person to propose that steady movement of water carves out gorges and canyons.
2. This became the inspiration for Charles Darwin’s theory of evolution.
3. Both of them engaged in thought experiments looking for how things around them attained their states and discovered underlying phenomena.
4. Similarly, Einstein, after reading about the experiments which concluded that the relative speed of light is always constant, engaged in thought experiments that eventually lead to the “Theory of relativity”.
5. The human brain is remarkably amazing in its ability to identify such patterns and discover underlying phenomena just by thinking.

Thought experiments on thinking

1. Experiment 1: It is easy to recite the alphabet going from A to Z, but difficult to do the reverse. The same experiment can be done for things like rhymes and poems. The conclusion is that Our memories are stored in sequential order. They can be accessed only in that sequential order.
2. Experiment 2: Try visualizing a person/situation which was encountered only once or twice, it is very difficult to visualize the details => Our memories are stored as a sequence of patterns, there are no images, videos, or sound recordings. Memories that are not accessed dim over time.
3. We can recognize even partial patterns with alterations , our recognition ability detects patterns that survive real-world variations.
4. Our conscious experience of our perceptions is changed by our interpretations , we continuously predict the future and hypothesize what we will experience and this influences the actual perception .
5. Routine procedures are stored as organized hierarchies in the human brain, the same ability is used for recognizing objects and situations.

A model of the neocortex

1. The Neocortex is responsible for hierarchical patterns of information and hierarchical thinking. Some scientists call it the “new brain” as opposed to the reptilian “old brain” which is more tuned towards short-term things like getting food, avoiding becoming someone’s food and having sex.
2. Humans have a really large forehead and large neocortex compared to other mammals. It has roughly 300 million pattern recognizers.
3. A human master in a particular field knows about 100, 000 chunks of knowledge.
4. Pattern recognition theory of mind - Neocortex has multiple layers of neurons, based on sensory inputs, some of the first layer neurons are triggered, and those that trigger beyond a certain threshold, fire the second layer of neurons, the second layer matches higher-level patterns than the first layer, the higher layer can send a back signal and reduce or increase the triggering threshold of the previous layers. This is the prediction and hypothesis part.
5. Memory is effectively a list of patterns. They will trigger with appropriate input leading to the recall of that memory. Since we capture patterns, our memory is only an approximation of events that happened in the past.
6. Learning - it’s difficult to learn too many conceptual levels simultaneously. It is difficult to train multiple layers simultaneously. We learn a level and as it stabilizes, we move to the next one.
7. Misunderstanding - A person tries to convey patterns in his neocortex to another person’s neocortex using “language” which itself is a set of patterns in the neocortex, these differences in patterns cause misunderstanding.
8. Directed thinking - where we consciously try to direct our thoughts toward understanding or solving a certain problem
9. Undirected thinking - where we experience sudden recollection of memories, triggers of which appear to be non-logical.
10. Confabulation - We subconsciously make up stories to justify our actions that cannot be explained logically. This is more pronounced in split-brain patients where the left and right hemispheres are not connected - leading to one part of the brain reacting and the other one confabulating to justify the action.
11. Culture, society, and profession predict certain norms, and this trains our neocortex to think in certain ways, this ensures social order but at the same time makes it difficult to think differently, which Darwin or Einstein did! In dreams, these norms are usually a bit relaxed.

The biological neocortex

1. The human brain is unusually large, its a cause of a higher maternal mortality rate among humans compared to other mammals and requires a pivoting gait which makes women biomechanically less efficient walkers than men.
2. The neocortex is a repetitive structure consisting of an “assembly of neurons” where each assembly is ~100 neurons and connections inside each assembly are similar. The connections between assemblies are dynamic, new ones are formed as needed and old unneeded ones are pruned away.
3. The neocortex is highly “plastic” - meaning if a part which deals with say, vision is damaged, slowly another part develops the lost set of patterns.
4. A genome has about 25 million bytes after lossless compression while total connections in the neocortex are ~ 10^15 => most connections are not determined genetically but built over time.
5. Over time, the field of AI (Artificial Intelligence) has developed the same set of techniques, that are believed to exist in the neocortex, to process real-world information like human speech and written language.

The old brain

1. Optic nerves have 12 output channels - one recognizes edges, another recognizes large areas of uniform color, and another focuses on background => effectively we only see patterns rather than exact details.
2. The human cochlea catches sound vibrations and extracts about 3000 bands of information.
3. The Thalamus process information coming from various parts of the body, including eyes and ears) before handing them over to the neocortex.
4. Neocortex on its own cannot do directed thinking, it requires inputs coming from Thalamus.
5. The Hippocampus is the area where short-term pattern forming happens, these patterns are transferred to the neocortex for the long term. Alzheimer’s disease attacks the Hippocampus first.
6. The cerebellum controls quick motions like catching a ball.
7. The old premammalian brain is addicted to pleasures like food and sex. Neocortex in mammals allows us to control primitive desires. Dopamine and Serotonin play a role in the feeling of pleasure.
8. Amygdala controls “fear”, that is flight or fight decisions - on detecting danger, it causes a sudden rise in blood pressure, heart rate, and respiration rate.
9. Feeling happens in both the old and new brain while thinking happens only in the new brain (“neocortex”).

Transcendent abilities

1. Emotional thoughts take place in spindle neurons - humans have a lot more of them than other animals. Newborns don’t have them but they are developed over the age of 4 months to 3 years. This is when a child learns emotions and morality.
2. The ability of the neocortex to master signals of fear from the Amygdala plays a role in confidence, organizational skills, and the ability to influence others.
3. Creativity - A key aspect of creativity is finding metaphors which the neocortex is good at. Learning new patterns from different fields helps in learning more metaphors, making the brain more creative.
4. Love - Phenylethylamine (PEA) causes the feeling of “love” - high energy level, focused attention, and craving to be with someone. Oxytocin encourages long-term bonding, that is, monogamous relations. Prairie vole is monogamous because of oxytocin receptors while montane vole engages in short-term relations because of lack of them.
5. Love in humans exists primarily to satisfy the need of the neocortex as primitive lust was sufficient for reproduction. A loved one becomes a major part of one’s neocortex and after spending decades together, a virtual other exists which can anticipate every move of the loved one. When we lose the person, we are still left with patterns in the neocortex which trigger, except triggers change from delight to mourning.

The biologically inspired digital neocortex

1. Neocortex replaces the process of slow evolution with fast learning and that’s one reason for the advancement of the human race. Since even a single human finds something new, everyone can learn that without relying on it appearing in the genetic code.
2. A digital neocortex will provide a factor of a thousand to a million speed up over the biological cortex.
3. Several attempts to do brain simulations at both the functional level as well as the molecular level are being done. By 2020, there will be sufficient computational power to simulate the human brain.
4. Techniques being used are neural networks, vector quantization (for sparse coding), HHMM (hierarchical hidden Markov models), and evolutionary genetic algorithms.
5. Watson, Google Translate, and Wolfram are some major works done in the direction of processing and generating real-world information.

The mind as a computer

1. The brain is slow but massively parallel.
2. In the human brain, 300 million pattern recognizers can be fired together.
3. The computers are fast but do not have sufficient parallelism.

Thought experiments on the mind

1. Consciousness is a heated topic of debate among philosophers. There are no agreements on “Are plants conscious?” or “Are babies conscious?”. The general agreement is that the “ability to act according to one’s free will” (implying nondeterminism) is consciousness.
2. Panprotopsychism says that everything is conscious, “humans are more conscious than a light bulb”.
3. The author predicts that by 2029, we can expect to see “digital consciousness”.
4. Western perspective - consciousness is an emergent property of the complex system.
5. Eastern perspective - consciousness is a fundamental property, the physical world only comes into existence through the thoughts of conscious beings.
6. The existence of “free will” is a hotly debated topic - the existence of free will requires non-determinism in actions and experts don’t agree on whether humans have free will, compared to say Watson, or are the actions predetermined. Some philosophers believe that the future is completely deterministic but complex enough to be unpredictable.
7. There are also disagreements on what constitutes identity - the author holds the position that a snapshot of the neocortex (or brain, in general) is a person’s identity, and hence, identity, in principle, is not unique and can be replicated.

The law of accelerating returns applied to the brain

1. Most technologies follow the S-curve, that is, slow start, rapid growth, and then maturity. But at the end of its life cycle, it’s replaced by something else, eg. Transistors replaced vacuum tubes.
2. Most technologies like processing power, storage capacity, brain imaging resolution, etc. are growing at an exponential pace and leading to a “Law of accelerating returns”. Hence, a digital brain will arrive faster than most people expect.

Objections

1. This chapter talks about objections raised to the previous work of the author - not much relevant to the rest of the book.