Monthly Archives: October 2013

Questioning the brain-computer metaphor

I have noted before that the brain does not do algorithms in the sense that computers do. We do not compute in a step-wise fashion, unless we are doing something consciously in a step-wise fashion. Take an example: to find if a number is even, first find the last digit, find if that digit is zero or is divisible by 2 without remainder, if so it is even and if not it is odd. If we consciously do this task stepwise, then those are the steps we will note consciously. 798 has 8 as its last digit and 8 is divisible by 2 therefore 798 is even. But of course we rarely go though the steps consciously, we look at the number and say whether it is odd or even. And we assume that we have unconsciously followed the appropriate steps. We have no proof that we have followed the steps – in fact we have no idea how we got the answer. There is no reason to assume that unconsciously we are following an algorithm.



Here is the abstract from a paper: Gary Lupyan; The difficulties of executing simple algorithms: Why brains make mistakes computers don’t; Cognition, 2013; 129 (3): 615.


It is shown that educated adults routinely make errors in placing stimuli into familiar, well-defined categories such as triangle and odd number. Scalene triangles are often rejected as instances of triangles and 798 is categorized by some as an odd number. These patterns are observed both in timed and untimed tasks, hold for people who can fully express the necessary and sufficient conditions for category membership, and for individuals with varying levels of education. A sizeable minority of people believe that 400 is more even than 798 and that an equilateral triangle is the most “trianglest” of triangles. Such beliefs predict how people instantiate other categories with necessary and sufficient conditions, e.g., grandmother. I argue that the distributed and graded nature of mental representations means that human algorithms, unlike conventional computer algorithms, only approximate rule-based classification and never fully abstract from the specifics of the input. This input-sensitivity is critical to obtaining the kind of cognitive flexibility at which humans excel, but comes at the cost of generally poor abilities to perform context-free computations. If human algorithms cannot be trusted to produce unfuzzy representations of odd numbers, triangles, and grandmothers, the idea that they can be trusted to do the heavy lifting of moment-to-moment cognition that is inherent in the metaphor of mind as digital computer still common in cognitive science, needs to be seriously reconsidered.”



The last sentence is particularly important. “… the metaphor of mind as digital computer still common in cognitive science, needs to be seriously reconsidered.”


Watching memories form

ScienceDaily has an item on memory (here) on a paper:


K. E. Moczulska, J. Tinter-Thiede, M. Peter, L. Ushakova, T. Wernle, B. Bathellier, S. Rumpel. Dynamics of dendritic spines in the mouse auditory cortex during memory formation and memory recall. Proceedings of the National Academy of Sciences, 2013; DOI: 10.1073/pnas.1312508110



Here is the abstract:


Long-lasting changes in synaptic connections induced by relevant experiences are believed to represent the physical correlate of memories. Here, we combined chronic in vivo two-photon imaging of dendritic spines with auditory-cued classical conditioning to test if the formation of a fear memory is associated with structural changes of synapses in the mouse auditory cortex. We find that paired conditioning and unpaired conditioning induce a transient increase in spine formation or spine elimination, respectively. A fraction of spines formed during paired conditioning persists and leaves a long-lasting trace in the network. Memory recall triggered by the reexposure of mice to the sound cue did not lead to changes in spine dynamics. Our findings provide a synaptic mechanism for plasticity in sound responses of auditory cortex neurons induced by auditory-cued fear conditioning; they also show that retrieval of an auditory fear memory does not lead to a recapitulation of structural plasticity in the auditory cortex as observed during initial memory consolidation.



In effect the researchers made microscopic ‘photos’ of the formation of memories and the weakening of the them plus the retrieval of the memories. The idea that ‘neurons that fire together wire together’ was clearly illustrated. The repeated conditioning increased the strength of the memory, while disrupting the conditioning decreased it, but did not destroy the memory. Retrieval of the memory did not change its strength. The notion that recall recapitulated the original memory formation was not supported.


What can be learned from social animals

Many would have us believe that it is a disadvantage is be social, generous, trusting, cooperative, unselfish or whatever it is called. But it is not a disadvantage, it is an advantage. Cooperation comes with costs like having to control cheaters but it is a very old and successful strategy. In this third post in the animal series, I look at social animals.



Comparative Neuro-biology 3: What can be learned from social animals?



Before we look at social animals, let’s look at very ancient cooperation. The difference between eucaryote cells and prokaryote ones is enormous. Prokaryotes such as bacteria are essentially just a lipid bag of water, salts, proteins, nucleic acid and carbohydrates. They have very limited internal structure and therefore very limited control over their metabolism. Eukaryote cells are also essentially a lipid bag but inside the bag there are many other bags. The DNA is inside a bag (the nucleus) and so access to it is controlled. The engines that burn sugar for energy are each in their own bags (the mitochondria) and the membranes are essential to the process of reaping energy. And so it goes for photosynthesis, protein manufacture, export from the cell and so on. How did eukaryote cells evolve? It seems to be that simple cells cooperated and eventually became so dependent on each other that they merged into a single more complex entity – one with extremely sophisticated control mechanism.


Eukaryotic cells differ from prokaryotic cells by their more complex intracellular organisation. Distinct cellular processes are compartmentalised. This improves efficiency but a problem emerges. Different compartments need to exchange specific molecules and certain molecules need to be exported to the cell exterior. Since most molecules are too large to directly pass through membranes, a mechanism is required to deliver the cargo. The 2013 Nobel Prize in Physiology or Medicine is awarded to Dr. James E. Rothman, Dr. Randy W. Schekman and Dr. Thomas C. Südhof for their discoveries of machinery regulating vesicle traffic, a major transport system in our cells. This represents a paradigm shift in our understanding of how the eukaryotic cell, with its complex internal compartmentalisation, organises the routing of molecules packaged in vesicles to various intracellular destinations, as well as to the outside of the cell.” (Nobel press release)



So… cooperation in biology is very ancient and is the foundation of multicellular organisms: plants, animals and fungi. But the idea of multicellular organisms itself requires cooperation. The individual cells have to give up any selfish sovereignty to the organism. The cells, tissues and organs have to cooperate or the organism dies. By staying and working together they can live outside the ocean on dry land, eat many more varied foods and all the other things that plants and animals can do that bacteria cannot. Every once in a while some cell goes maverick and attempts to escape the multicellular restriction and we have a cancer. Most cells do not make it to the stage of a cancer because the organism has methods of finding and killing cells that cheat. Cellular slime molds are right on the edge of the divide between multicellular and single celled organisms. How do they deal with cheaters?


Much of what we know about the evolution of altruism comes from animals. Here, we show that studying a microbe has yielded unique insights, particularly in understanding how social cheaters are controlled. The social stage of Dictylostelium discoideum occurs when the amoebae run out of their bacterial prey and aggregate into a multicellular, motile slug. This slug forms a fruiting body in which about a fifth of cells die to form a stalk that supports the remaining cells as they form hardy dispersal-ready spores. Because this social stage forms from aggregation, it is analogous to a social group, or a chimeric multicellular organism, and is vulnerable to internal conflict. Advances in cell labeling, microscopy, single-gene knockouts, and genomics, as well as the results of decades of study of D. discoideum as a model for development, allow us to explore the genetic basis of social contests and control of cheaters in unprecedented detail. Cheaters are limited from exploiting other clones by high relatedness, kin discrimination, pleiotropy (multiple effects of a gene), noble resistance, and lottery-like role assignment. The active nature of these limits is reflected in the elevated rates of change in social genes compared with nonsocial genes. Despite control of cheaters, some conflict is still expressed in chimeras, with slower movement of slugs, slightly decreased investment in stalk compared with spore cells, and differential contributions to stalk and spores. D. discoideum is rapidly becoming a model system of choice for molecular studies of social evolution.” (Strassmann 2011)



Then there is symbiosis. Organisms that are separate but live in intimate contact - corals and lichens for example. Lichens are an association of an algae and a fungus – they are successful on rocks that support nothing else. Corals are an association of the invertebrate coral polyp and an algae – its reef colonies are the foundation of a very successful ecosystem (at least until recent ocean changes). There are a lot of different types and degrees of symbiosis. It is a successful way of life.



Social insects (ants, termites, bees, wasps) are amazingly successful. Their cooperation is very evident and the obvious reason for their success. The social vertebrates are also successful. Throughout biology, where ever we look we find cooperation. From the tiny cells and their physiology, to organisms, to cooperating organisms, even to ecosystems, we find cooperation succeeds. So when someone says that cooperation is a strategy that fails – they are wrong. The proof that cooperation works is all around us. What are the game theorists missing?


With new insights into the classical game theory match-up known as the “Prisoner’s Dilemma,” University of Pennsylvania biologists offer a mathematically based explanation for why cooperation and generosity have evolved in nature. …The Prisoner’s Dilemma is a way of studying how individuals choose whether or not to cooperate. In the game, if both players cooperate, they both receive a payoff. If one cooperates and the other does not, the cooperating player receives the smallest possible payoff, and the defecting player the largest. If both players do not cooperate, they receive a payoff, but it is less than what they would gain if both had cooperated. In other words, it pays to cooperate, but it can pay even more to be selfish…After simulating how some generous strategies would fare in an evolving population, Steward and Plotkin crafted a mathematical proof showing that, not only can generous strategies succeed in the evolutionary version of the Prisoner’s Dilemma, in fact these are the only approaches that resist defectors over the long term. “Our paper shows that no selfish strategies will succeed in evolution,” Plotkin said. “The only strategies that are evolutionarily robust are generous ones.”…. “When people act generously they feel it is almost instinctual, and indeed a large literature in evolutionary psychology shows that people derive happiness from being generous,” Plotkin said. “It’s not just in humans. Of course social insects behave this way, but even bacteria and viruses share gene products and behave in ways that can’t be described as anything but generous.” “We find that in evolution, a population that encourages cooperation does well,” Stewart said. “To maintain cooperation over the long term, it is best to be generous.”(Steward 2013)



(Aside: I have to say that the Prisoner’s Dilemma is not life. When there is a supposed simulation of the real world, the question to ask is exactly when and where this is a valid simulation rather than a useless mathematical/logical formula. That cooperation works and is wide-spread is an established fact, why this might be is the question that the game/simulation research is about.)



The problem with the Prisoner’s Dilemma as a model is that there is no communication and communication is key to cooperation. All the examples of cooperation have some level of communication. It can be physical contact, chemical exchanges, smells, visual signs, sounds; but there must be communication, an awareness of what the partner/s are doing. Communication is necessary for a level of ‘trust’, including the identification of a partner as legitimate at its simplest. No communication; no trust; no cooperation. Communication is not some little add-on but something important that living things do, internally and externally.



There are very impressive examples of cooperation in mammals, especially the hunting strategies of various dogs, cats and dolphins. We find that social mammals have ways of communicating that are similar to our non-verbal communication – no real difference of kind. Probably the oldest non-verbal channel is posture. When I used to give talks on non-verbal communication, I would point out that the different between taking an upright, head up stance and taking a low, head down stance is extremely old and very obvious in reptiles as well as birds and mammals. The tall pose is aggressive and the crouching pose is submissive. Postural communication is very clear in dogs, horses, primates – and that includes humans. The dog’s play-bow is a good example. It says, “What I do now is not meant to be taken seriously, it is just play. Come play with me.” Posture even can work between species. Apparently it works for huskies and polar bears, as has been shown on YouTube. “Here comes a wild polar bear cut off from his normal seal diet by the water-not-yet-ice … he comes upon a husky tethered in the snow … it looks like lunch time for the bear. … It is not hostility being exchanged between these two… note the the polar bear’s eyes are soft, the husky’s ears are back, his hair is flat and his mouth is open without showing fangs – just a few moments before, as the bear came into view, the husky was in a crouched (play) bow and a wagging tail… something beside attack is on their minds… two carnivores facing each other and, instead of a bear’s predatory attack to feed his hunger, something magical happens” … (see pictures at nifplay below)



I could give a long list of animal communications including everything from bacteria to apes but I will not. I think anyone would agree that communication is common among animals. The point I am making is that without communication we cannot have cooperation and without cooperation we cannot have social groups. Without social groups, we do not have culture. Culture is the big prize. Culture is what humans have in abundance and other social animals have only small amounts of. Culture is what allows us to visit the moon. We have an explosion of culture and that is because we have a great advance in communication, our languages.



Why do other animals such as the apes have communication and cooperation and even a little culture, but they do not have language and with it no explosion of culture? We could just throw up our hands and say, “that’s evolution”. But actually it is a very serious question. When we have chimps and bonobos in captivity and familiar with humans, it is possible to teach them rudimentary language using hand signs or computer tools. So it seems it should have been possible for them to have developed protolanguage and then like humans to have found it so useful that both biological and cultural evolution would have favoured it. But this did not happen. There are a number of other animals that ‘might’ have developed language but didn’t, although they have extension communication and cooperation – elephants and dolphins come to mind.



Blair Bolles in his blog Babel’s Dawn examined the origin of language for about 7 years. He came very close to the heart of the problem in the ideas: that language is dangerous as well as advantageous; and, that group evolution is possible. It is not always in an individual’s best interests to share secrets, let alone broadcast them. Animal communication seems to be limited to very stereotyped messages. Given non-group evolution it may be impossible for language to be selected for because it is often not to the individuals advantage. It is very difficult to show group selection in biological traits but cultural evolution is very obviously a result of group selection (it being groups and not individuals that have culture). We are talking about a little jump from the realm of predominately biological evolution to predominately social evolution. The bonobo is on the one side of that gap and we are on the other.


We know that captive chimpanzees can learn to use words and phrases but in the wild they never tell one another anything. They communicate to control. This kind of discretion is easy to explain in terms of individual selection. A chimpanzee who knows where there will be some ripe fruit has an advantage over its fellows. A chimpanzee who blabs his news has given up an advantage. The fitness score of the chimpanzee who keeps secrets is almost certainly higher than the blabbermouth’s score. Thus, even though groups might benefit from language, it is not going to evolve among chimpanzees. This kind of reasoning makes it easy to explain why language never evolved with other species, and hard to explain why humans have such a hard time keeping secrets. (see Bolles’ post below)



We have come full circle: communication facilitates cooperation, which facilitates culture, which facilitates communication and cooperation.



Image: Orpheus charming the animals by Jacob Savery




Eukaryote controls - Press releases about Nobel Awards


Strassmann JE, Queller DC; Evolution of cooperation and control of cheating in a social microbe; Proc Natl Acad Sci U.S.A 2011, 108 Suppl 2:10855.62. doi: 10.1073/pnas.1102451108


University of Pennsylvania material (2013), Biologists show that generosity leads to evolutionary success


Play signals -


Origins of language -



Animals have the behavior they need

This is the second post in a series about animals. For many years (centuries) there has been the idea that humans have many behaviors and skills that animals don’t. Slowly the list has become shorter and shorter. Although we do act very differently from other animals, this difference is largely a cultural one rather than a biological one. I recently wrote a piece on the immense difference between ourselves and other animals in cultural evolution, why are we different (see link below). This current posting is about the brain’s non-cultural skills.



Comparative Neuro-biology 2: Animals have the behavior they need



Basically we can assume that almost all animals are adapted to their niche and have the abilities they need to in order to survive in that niche. They have behaviors to find food, find mates, protect themselves and so on. But we cannot be sure of the abilities that are possible but not called upon. For example, humans have echo location abilities but you have to look far and wide to see anyone use that ability, except the blind, of course. “…This shows that anyone can learn to analyze the echoes of acoustic signals to obtain information about the space around him. Sighted people have this ability too; they simply don’t need to use it in everyday situations. Instead, the auditory system actively suppresses the perception of echoes, allowing us to focus on the primary acoustic signal, independently of how the space alters the signals on its way to the ears.” (Wallmeier 2013) The suppression allows us to concentrate on the sounds important to us but it can be reversed.



So we have the situation where dolphins and bats have converging evolution for a very effective sonic location system. They share adaptations with each other that their closer relatives do not have. There are probably only certain ways the mammals can develop such a system. But that does not mean that the sort of echo location humans are capable of is not wide-spread in mammals. Given an evolutionary pressure to use echo location, probably most animals could start with a rudimentary ability such as ours and evolve an excellent ability such as bats and dophins have. It is difficult to know what abilities an animal has unless we can devise the training and testing to bring it out. It is obvious that if humans are blind they almost automatically learn to echo locate and if they are not blind, they do not even know they are capable of it. Most of us cannot swing through trees like an orangutan but there are human trapeze artists; most of us cannot dive like a seal but there are human pearl divers. We cannot look at animals just going about their normal lives and say that they cannot do some other specific thing.



What talents of animals have surprised us? Alex the parrot investigated by Irene Pepperberg could count and add objects or arabic numerals. Alex learned names of categories of objects and characteristics such as colour. He also carried on simple conversations. Pepperberg made him a co-author on the last paper about the research– showing that she viewed him as an active participant in the research. Alex might seem very unusual but parrots and crows are groups that show particularly high intelligence. “Clearly, animals know more than we think, and think a great deal more than we know.” (Alex and me).



The list of abilities found amongst parrots and corvids is long and includes: tool use, tool making, serial use of tools, problem solving, puzzle solving, simple counting and arithmetic, vocal learning, schooling of offspring, learning from one another, communicating specific information, point/gesture with beak/wing, remembering individuals (including human ones), remembering hiding places, remembering events, designing nests, holding a grudge, mourning their dead, recognizing themselves, patiently delaying gratification, deceiving others, acting collectively for protection, having personal names, using causal reasoning, using transitive logic, using inference by exclusion, using rule abstraction. (sources below) Similar lists can be compiled for primates and for whales/dophins. Elephants have an impressive list. Even the dog, as a result of long association with humans, has some very unusual skills. And song birds have specific abilities that overlap with human language learning. What is missing from these lists is language proper (whatever that means these days). All sorts of communication is on the lists, some of it quite sophisticated and approaching what we would call language. Other animals also do not use and control fire. At least we have not found any ways of bringing this out in other animals.



Behavior is the outward effect of what is happening in the animal’s brain and that is what is interesting to the neuro-scientist. The questions are about what is happening in the animal brain – ours and other animals’. The comparisons are hampered by the ways we view our thought differently from their thought. We feel we make conscious plans and decisions, which are thought out more or less logically. We are surprised when we are confronted with experiments that show that the conscious thoughts are ‘after the event’ of unconscious planning and decisions. We are surprised when animals appear to enjoy conscious experiences. There is no reason I can think of for rejecting the assumption that we think like other animals and other animals think like we do. We all have conscious experiences and we all have them ‘after the event’ of unconscious thought. It is the same scientific problem to solve but if we make this assumption then there is a lot more information available to work with. For any ability, we should assume that for vertebrates, differences of kind are very rare, while differences of degree are very common.



Image: Paradise landscape with the fall by Jan Breughel








A recommendation

Mo Costandi writes a blog, neurophilosophy, for the Guardian, which is always worth a read. Recently he wrote a book - 50 Human Brain Ideas You Really Need to Know (here). In his blog he has looked at some of the ideas in the book, the latest is the differences and non-differences between the brains of women and men. (here)

If you are having difficulty separating the good from the bad in the popular media’s coverage of neuroscience, this a a must have book for you. And, of course, it is a good read even if you are not confused. The world needs a guide like this to avoid the worst of bad reporting and silly writing. It sets out the current scientific consensus.

All animals are built on the same plan

Animals entering Noah’s ark - Brueghel the Elder


I plan to write a series of posts on animal research. The idea came about when I was thinking about the way we have been told for years not to be anthropomorphic. There is an opposite word, zoomorphic : “The tendency of viewing human behaviour in terms of the behaviour of animals, analogous to anthropomorphism, which views animal behaviour in human terms.” This idea has also been frowned upon. Why are we cautioned to avoid understanding animals by seeing them using human concepts and understanding human by seeing them using animal concepts? These restrictions are slowly losing ground but they still appear in our books, magazines and newspapers fairly regularly. So this series is on comparative neurobiology.

Comparative Neurobiology 1: All animals are built on the same plan

A good place to start is near the beginning, before active animals. (It was active animals that required the development of a nervous system.) Neither yeasts nor sponges have nervous systems but they have much of the chemical machinery to make a neuron and its synapses. They do not use these chemicals together to make a synapse but use them separately for different tasks. When animals with nervous systems arose they already shared these basic chemical building blocks. All animals are inheritors of the chemical endowment for a nervous system to use and modify as needed by their way of life.

  • Jon Lieff has some interesting blogs on this including (see below). “The synapse first appeared in evolution approximately 700 million years ago, with the first circuits of neurons soon after. But, the proto-synapse occurred over a billion years ago in microbes.” Synapses are very complicated (exceptionally so, I would say) but their components existed for other uses.
  • Mechanisms enabling one cell to influence the behavior of another almost certainly existed in the world of unicellular organisms long before multicellular organisms appeared on earth. Evidence comes from studies of some present-day unicellular eukaryotes such as yeasts.” (Alberts 1994).
  • Of course, there have been modifications over all these years. “We studied around 600 proteins that are found in mammalian synapses and were surprised to find that only 50 percent of these are also found in invertebrate synapses, and about 25 percent are in single-cell animals, which obviously don’t have a brain….The number and complexity of proteins in the synapse first exploded when muticellular animals emerged, some billion years ago. A second wave occurred with the appearance of vertebrates, perhaps 500 million years ago.” (Emes 2008) This is not as clear cut a progression as it may appear – it may not even be a progression. It may be that if they had started with all the proteins in invertebrates’ synapses, they might have found 50% of them in mammals and a slightly different 25% in single-celled animals.

The similarity in proteins implies a genetic similarity. The take-home here is that there is a very strong family resemblance across all animal nervous systems even if they may look different on the surface.

How similar are all vertebrate nervous systems? All vertebrates have a spinal cord and at the front end of the spinal cord the brain develops. Three areas appear in early embryos: fore, mid and hind portions of the brain. The same ventricles appear. Different parts grow at different rates so that the end product looks different but they all start with a very similar basic architecture shared by fish, amphibians, reptiles, birds and mammals. This implies that the developmental signals prompting cells to migrate, differentiate and connect have a strong family resemblance, a conserved genetic plan. What the vertebrate scheme seems to be is that: the fore-brain (cortex, thalamus, basal ganglia and some other structures) receives sensory information and has the highest integration of information; the mid-brain coordinates reflex responses to sensory information; the hind-brain has reflex control of things like respiration and heart rate. But, for instance, the cerebellum is important to coordination of sensory, motor and cognitive dexterity in many vertebrates, so the hind brain is not excluded from complex activity.

For many years it was thought that the neo-cortex was found only in mammals but it is now known that birds and reptiles have similarly functionally connected neurons to those in the neo-cortex. In other words the non-mammals can make the similar connections to do similar cognition as mammals but with a structure that does not look like the neo-cortex. “Both the mammalian neocortex and a structure in the bird brain called the dorsal ventricular ridge (DVR) originate from an embryonic region called the telencephalon. But the two regions mature into very different shapes, with the neocortex made up of six distinct cortical layers while the DVR contains large clusters of neurons called nuclei.” (Dugas-Ford 2012). All vertebrates share the same fundamental developmental plan for the brain.

The brains of mammals are very similar. Mice for instance make good laboratory subjects because their brain are close enough to our own to mimic our diseases of the brain. Genes can be transferred from humans to replace the homologous genes in the mouse and the human genes work well in the mouse. Can there be a better test of physiological similarity? “New mouse strains engineered to express human genes related to mental disorders are being developed under a recently-launched grant program from NIMH’s Division of Neuroscience and Basic Behavioral Science. The new models are designed to help scientists understand the molecular workings of variations in genes that may predispose for – or even help protect against – illnesses like depression, bipolar disorder and schizophrenia. They will also explore how duplications or the differences in the amount of genetic material affect brain function, and how genes influence response to treatments. The new studies follow a spate of recent discoveries using such mouse models to replicate features of mental and developmental disorders.” (NIMH 2008)

Of course primates, particularly great apes and very particularly chimpanzees and bonobos are extremely similar to humans. Our brains are not identical but they share a great many fine details. There needs to be some caution in assuming that primates will always be closer to us than other animals. When we look at whales, dogs, elephants, bats, crows, parrots we find that there are some striking similarities with us but I will discuss these in another posting that looks at behavioural similarities.

We have only a few million years of separation from chimpanzees and bonobos. These three species are so close that if they were almost any other group, they would be put together in one genus. For example the Canus genus contains 10 species: various wolves, dogs, jackals and coyote – that is certainly a wider range than the 3 species: human, chimpanzee and bonobo which are divided into Pan and Homo.

So given the anatomical, biochemical, physiological, developmental and genetic similarities between us and other animals, why should we not look at them to understand ourselves and look at ourselves to understand them? The great many experiments and observations that have been done on the brains of other animals have been invaluable and this research will continue – because anthropomorphism and zoomorphism are useful legitimate tools.

Image: Jan Breughel the Elder – The Entry of the Animals into Noah’s Ark – Google Art Project


Searching for Mind blog,

Alberts B, Bray D, Lewis J, et al. Molecular Biology of the Cell. 3rd edition. New York: Garland Science; 1994. General Principles of Cell Signaling. Available from:

R Emes etal. Evolutionary expansion and anatomical specialization of synapse proteome complexity. Nature Neuroscience 11, 799 - 806 (2008)

J Dugas-Ford etal. Cell-type homologies and the origins of the neocortex. PNAS October 16 2012 vol.109 no 42

NIMH press release, Mice Expressing Human Genes Bred to Help Unravel Mental Disorders