In her third lecture, Dr Susan Greenfield asks if the brain works like a computer, or a bubbling cauldron of chemicals, and considers how nerve signals actually work.
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This lecture was filmed at the Ri on Thursday 22nd December 1994.
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If the brain were pulled apart until we arrived at its most basic component, we would finally come to the brain cell, or neuron. One of the readiest ways of studying brain cells at work is to see how they respond to identified events in the outside world, such as a sight or a sound. Cells in the human retina convert the physical properties of a visual image into nerve signals. From the retina inwards
into the brain, separate relays of neurons process in parallel different aspects of that image, such as its shape, colour and movement. However, it is still a mystery how the whole visual picture is recognised as a cohesive pattern. But what really happens when a neuron 'responds' to a signal from another cell? When a neuron needs to pass on a specific signal, it generates an 'action potential'. Action potentials are usually very short, some one to two milliseconds in duration. For this brief period, the ions in the brain, most basically sodium and potassium, redistribute themselves across the membrane wall of the neuron to cause a sharp change in potential difference. This potential difference is then propagated down the length of the neuron to where it reaches out to the next cell. Once the end of the neuron is activated by the action potential, it
releases a chemical messenger, a 'transmitter'. This transmitter diffuses to the next cell and binds to it on special target proteins. Once the transmitter binds to the protein, ion channels in the second cell will open, so causing a change once again in the potential difference. In this way neurons communicate by an electrical signal encoded by the first cell into a chemical one, which is decoded
back into an electrical signal by the second cell. A wide variety of drugs can interfere with this process and consequently change dramatically how we think and feel.
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Then Dr Susan, now Baroness Greenfield (b.1950), presented the 1994 CHRISTMAS LECTURES as a five-part series, entitled 'Journey to the Centres of the Brain'. Our brains are ourselves. Every emotion, prejudice and hope is grounded in a molecular scenario somehow and somewhere in the secretive, silent organ between the ears. These lectures will explore what we know, and what still mystifies us, about the workings of the brain. Starting with no prior knowledge, we shall see what the brain looks like, how it generates electricity, and how it uses chemicals to process information. We shall be left with the thought that we know a great deal about how different brain regions function, but how such regions work together to generate a cohesive, individual individual consciousness, remains a tantalising puzzle.
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