Editor's comment

Patricia Smith Churchland is Chair of the Philosophy Dept. at UCSD. Her work relating recent brain studies with philosophy is extensive.

Reading on: Neuroscience and progress

Where it came from and where it is going.

Churchland, Patricia Smith Brain-Wise: Studies in Neurophilosophy The MIT Press, Cambridge, MA 2002 [abstract – 580 words]

Why did progress in neuroscience lag so far behind progress in astronomy or physics or chemistry? The problem is that brains and neurons are exceedingly difficult to study. Neural networks, ionic synapse transfer, and tools like the electron microscope and functional magnetic resonance imaging (fMRI) were unknown until relatively recently.

There are about 10^5 neurons per cubic millimeter of cortical tissue and about 10^9 synapses. To begin to understand the nervous system it is essential to know how neurons work. That entails the knowledge of electricity. What makes brain cells special is their capacity to signal one another by causing fast micro changes in each others’ electrical states. Movement of ions, such as Na+, across the cell membrane is the key factor in neuronal signaling, and hence in neuronal function. In the 1970s the role of specific neurochemicals in signaling and modulating neuronal function was beginning to be unraveled, and associated with large-scale effects such as changes from being awake to being asleep, to memory performance, to pain regulation, and to pathological conditions.

Many fundamental questions about how the nervous system works remain wide open. In particular, bridging the gap between activity in individual neurons and activity in networks of neurons has been difficult. Macro level operations depend on the orchestrated activity of many neurons in a network, and presumably individual neurons make somewhat different contributions in order for the network to achieve a specific output.

It is important to understand that none of the imaging techniques measure neuronal activity directly. They track changes in blood flow (hemodynamics). Because the evidence suggests that localized increases in blood flow are a measure of local increases in neuronal activity (more active neurons need more oxygen and more glucose), they are believed to be an indirect indication of changes in levels of activity in the local neuronal population.

Many “psycho illnesses” are now recognized as defects in brain function. For example, the discovery that highly addictable subjects have a gene implicated in the quirks of their dopamine reward system begins to hint that we will want to reconsider what exactly having or lacking will power comes to.

That the story structure giving shape to traditional philosophical inquiry may itself evolve, perhaps quite profoundly, accordingly presents an even deeper challenge to those who wish to isolate philosophy from science.

If we allow discoveries in neuroscience and cognitive science to butt up against old philosophical problems, something very remarkable happens. We will see genuine progress where progress was deemed impossible; we will see intuitions surprised and dogmas routed. We will find ourselves making sense of mental phenomena in neuro-biological terms, while unmasking some classical puzzles as pre-neuroscientific misconceptions.

Neuroscience has only just begun to have an impact on philosophical problems. In the next decades, as neurobiological techniques are invented and theories of brain function elaborated, the paradigmatic forms for understanding mind-brain phenomena will shift, and shift again. These are still early days for neuroscience. Unlike physics or molecular biology, neuroscience does not yet have a firm grasp of the basic principles explaining its target phenomena. The real conceptual revolution will be upon us once those principles come into focus. How things will look then is anybody’s guess.