Our Complex Brains: Lessons from Phrenology
This is your brain on science: it is too complex for simplistic diagrams. Back in the 19th century, the “science” of phrenology was in full swing. Phrenologists divided the brain into more than two dozen regions of “mental faculties” that controlled such things as instincts for eating and sex, sensation of color, language ability, and even moral and intellectual qualities such as love, wisdom, poetry and ability to ponder metaphysics. Once these regions were mapped out, some practitioners believed they could rate your abilities by feeling the bumps on your head. These beliefs quickly degenerated into ranking races and groups as intellectually superior or inferior.
Even into the late 20th century, it was common for textbooks to subdivide the brain into distinct functional regions. There is observational support for this: we know that sensory organs (eyes, ears) map to localized regions in the brain, and that sensory and mental disorders can be traced to sites of damage or poor development. In addition, the brain does have a noticeable structure: a stem, a hypothalamus, white matter, gray matter, the cerebral cortex and other recognizable parts. The left and right hemispheres have different properties – though not to the degree to support popular misconceptions that women are right-brained and men are left-brained, or that artists are right-brained and scientists are left-brained.
Neuroscience of the brain is a rapidly growing field. The brain can be approached through multiple paths. Scientists can strive to understand the workings of individual brain cells, such as the varieties of neurons and glial cells. Others can monitor brain waves during various activities. The effects of diet, exercise and sleep can be measured. Comparative anatomy can compare and contrast brain structure and function in lab rats, cats, monkeys and humans. And the effects of brain damage can be ascertained. Our ability to probe the brain’s secrets have become increasingly sophisticated with MRI, fluorescent proteins, genetic engineering and more.
We have learned much, but there is a vast undiscovered landscape within the brain still to be understood. Some idea of the status of brain research can be found in a couple of recent papers. They show one clear lesson: that ideas about localized functional areas are far too simplistic. Phrenology was wrong. The entire brain is in constant communication: function cannot be restricted to distinct regions, and we still have the profound mind-body problems about the seat of consciousness and intellect. Actually, phrenology might have served as a useful heuristic device, an attempt to bring order out of complexity, but it is dismissed as pseudoscientific today. Here are some of the recent indications that more than we can imagine is going on at the nexus of structure and function.
- PhreNOlogy: Robert Knight in Science June 15 commented about recent papers that “debunk phrenology.”1 His first paragraph pretty much sums up the verdict:
Systems neuroscience aims to understand how billions of neurons in the mammalian brain support goal-directed behavior, such as decision making. Deciphering how individual neurons respond to sensory inputs or motor decisions has focused on delineating the neural basis of these processes in discrete regions of the brain’s cortex, and has provided key insights into the physiological basis of behavior. However, evidence from neuropsychological, electrophysiological, and neuroimaging studies in humans has revealed that interactions between widespread neural regions in the brain underlie fluid, organized behavior. Two papers in this issue, by Womelsdorf et al. on page 1609 and Saalmann et al. on page 1612, and a recent paper in Science by Buschman and Miller, unravel the details of these interactions by assessing the simultaneous activity of neurons in multiple sites of the mammalian brain. The studies show that network interactions among anatomically discrete brain regions underlie cognitive processing and dispel any phrenological notion that a given innate mental faculty is based solely in just one part of the brain.
Researchers found multiple regions of the brain responding to the same visual tasks in monkeys. There appeared to be feedback between widely-separated regions. Some of these regions communicate at different frequencies of oscillations. The current picture is one of neural networks involving the entire brain, not just localized regions responding to sensory inputs.
- Primer: Stewart Shipp gave readers of Current Biology a primer on brain structure.2 He began by giving a reason why our gray matter has its odd, wrinkled shape. It provides efficiency in wiring:
The grey matter of the cerebral cortex is a convoluted, layered sheet of tissue, 2-3 millimetres thick in man but with a surface area of several hundred square centimetres. This is not an adaptation to promote gaseous exchange, or heat loss – rather, if the grey matter is compact in at least one dimension, it is outgoing axons that may readily escape it; once outside, they club together and form the cortical white matter. If grey and white were intermixed, the average separation of neurons would be greater, creating extra neural ‘wiring’. The speed of cortical computation would suffer accordingly.
The principle of economic wiring can also be invoked to account for regional specialisation of function across the surface area of the cortex. Put simply, neurons performing similar roles need to communicate, and do so more efficiently if nearby.
Thus the reason for regions of function. Nevertheless, it’s not the whole story: there is also a great deal of cross communication between regions, as well as cross-level communication within regions.
Shipp described how columns of neurons (perpendicular to the layering) were found to correspond to distinct parts of the body: a patch of skin, for instance, might activate a column of neurons within the motor region. But there is also communication parallel to the layering across columns, and this is where the simple idea of distinct regions breaks down:
Moving tangentially through the sheet (parallel with the plane of layering) the discovery was that neighbouring columns have neighbouring receptive fields � the ensemble of columns ultimately giving rise to a cortical map of the relevant sensory surface. In sensory cortex, this engenders the ‘one map, one area’ principle for parcelling the cortical surface into discrete areas, each of which is thought to have some nuance of functional specialisation. Cortical areas are richly interconnected – with each other and with subcortical structures – and the layering of the cortex reflects the radial organisation of all these input-output relationships. Indeed, the layered pattern is rather uniform over the expanse of the sheet, as if to serve basic ‘housekeeping’ operations that generalise across cortical applications as diverse as colour vision, speech and music.
Some regions are well known – the primary motor cortex and the primary visual cortex – but “These variations in cortical architecture have long been treated purely cartographically, betraying a lack of any analytic insight into the way different applications might modulate layer structure and function,” he said, further debunking phrenology. “This is largely because, as documented below, our appreciation of layers is still rooted rather more securely in anatomical than physiological cortical characteristics.” The whole picture requires both.
We know more about the visual cortex because it has received an order of magnitude more study than other regions of the brain. The emerging picture is more of multiple layers of structure and function, with cross-communication and feedback between all of them. The brain must be seen as an entire network of interacting systems. Yes, areas with discrete functions tend to be collocated, but the brain as a system cannot be carved up into chunks.
This brings us to Shipp’s tongue-in-cheek conclusion: the brain is your fiend.
The complexities of cortical circuitry are nothing short of fiendish, and the problem of integrating genetic, morphological and physiological details from diverse cortical areas and across diverse species is a worthy challenge to the burgeoning science of neuroinformatics. Though inconsistencies abound, the fact that some trans-areal, trans-specific generalisations are possible, and justified, is a quite remarkable observation. Following the strategy of ‘know thine enemy’, it appears that the cortical fiend has some interesting habits, which we can usefully begin to tag with some shorthand, functional labels.
“Neuroinformatics” – a very suggestive word.
Knight ended his review with a comment about neuroinformatics – one of the most baffling questions of all:
One mystery remains: How is information in oscillatory activity encoded? The individual spike train rate (the number of times a neuron fires each second) or spiking frequency (the rhythm at which a neuron fires) is not sufficient for coding the vast array of processes that underlie perception, memory, or decision making. Nevertheless, the three groups have laid the groundwork for deciphering this neural code.
The mind-body problem, therefore, is still with us. How does the soul, the mind, consciousness, intellect, wisdom, morality, and abstract reasoning correlate with a physical object, the brain? The problem becomes apparent as you “think about thinking about“ this right now. Your eyes are receiving light waves. Those inputs are traveling to your optic nerve, and to the visual cortex of your brain. Neurotransmitters are being secreted across synapses. Billions of cells are involved in the process of reading these words. Yet writer and reader each have a sense of communicating information through space. You may be across the planet from the one who wrote this. We sense ourselves reasoning about abstract concepts that cannot be reduced to atoms and molecules. Information is being conveyed and stored. Values are being expressed. That information can cause the reader to command body parts to move in response. Where is the connection between concept and atom, between mind and molecule? The mysteries are profound. They have occupied the minds of the world’s greatest philosophers for thousands of years. One thing is clear: don’t expect a simplistic model like phrenology to satisfy the requirements for explanation.
1Robert T. Knight, “Neural Networks Debunk Phrenology,” Science, 15 June 2007: Vol. 316. no. 5831, pp. 1578-1579, DOI: 10.1126/science.1144677.
2Stewart Shipp, “Structure and function of the cerebral cortex,” Current Biology, Vol 17, R443-R449, 19 June 2007.
If you were living in the 19th century, would you have been swayed by the claims of the phrenologists? Would they have influenced you to think they were onto something scientific? Would you have come in for a sitting for a skilled phrenologist to feel the bumps on your head, and tell you about your abilities? Well, you would have been misled. One can only wonder about the mischief done to victims of this simplistic pseudoscience – students influenced toward wrong careers based on the verdict of a phrenologist that he or she was poor at art or wisdom or abstract reasoning; false pride given to fools who were told they were intellectually superior; and worst of all, whole classes of people who were deemed unfit or defective based on their skull features. The Rwandan genocide can be traced to phrenology. The Dutch began a racist segregation of two very similar tribes, the Hutus and Tutsis, based on alleged intellectual differences. Those tensions grew until the genocide of 1994 that killed nearly a million people (see Touchstone Magazine).
Yet are we immune today? We still fall for the same old tricks. Here’s a simple one: the brain of a stegosaurus was proportionally small for its body size, therefore stegos were stupid. While that probably was true in some sense, do you see the hidden assumption? The statement assumes that bigger is better. Sometimes more power and efficiency can occupy a smaller space. Your small laptop computer is more powerful than a bulky 1970s mainframe. Maybe the stego had much more efficient and compact neurons than we do, or a better organized neural network. Who knows; maybe they were actually good at philosophy but didn’t leave any written records. We jest, but beware the logical traps of begging the question and glittering generalities. Evolutionary paleoanthropologists are often guilty of this (e.g., 01/27/2004).
A study of the history of science is valuable as a warning about pitfalls in reasoning that can become part of an accepted cultural mythology, sometimes for decades and centuries. OK, so phrenology is wrong. Don’t think that today’s neuroscientists and psychologists have it right. The myth of progress tempts us to assume that whatever is newer is better. Yes, we have better tools and a much more precise observational database about the details of the system, but the complexities of the mind and the brain remain vast and seemingly intractable. Today’s evolutionary neuroscientists are trying to tell us that love, altruism and morality are due to brain mutations in our primitive ancestors. To what mutations do they attribute that conclusion?
Shipp advises us to know the enemy and attack the cortical fiend inside us. In some respects, given what we know of human nature (1, 2, 3), that metaphor might generate some productive heuristics.