As you read these very words, you are receiving a rich variety of sensory signals – sound pressure at your eardrum, light intensity falling on your retina, sensations from the tip of your toe – all reaching your brain through voltage pulses called action potentials or ‘spikes’ transmitted via millions of sensory neurons. Brain, considered to be the seat of Mind & Consciousness, is in many ways the final frontier of scientific research. Theoretical or Computational Neuroscience aims to study how our brain encodes, performs computations on, and then decodes information from these ‘spikes’ in order to represent, interpret and understand the sensory world, and to initiate suitable actions (for eg., to move muscles in your eye to change the position of the eyeball) via information transmitted from the brain to the motor neurons.
The starting point of this study was the ground-breaking experiments of E. D. Adrian in the 1920s, who was the first to employ sensitive instruments to record from single axons of sensory receptor neurons (the first neurons he recorded were from stretch receptors in the muscle of the frog). These neurological signals, or ‘spike sequences’ are the language of the brain and nervous system, both for its internal communication and computation, and for external interaction with the outside world. The Central Questions Some of the central questions addressed by Neuroscience are – 1) How is information of the continuously varying external stimulus encoded (Neural Code) in to a ‘spike sequence’? 2) What is the information rate and coding efficiency of this Neural encoding? 3) How does the brain perform computation on these neurological signals? 4) Natural conditions impose a lot of noise on the ‘spike sequence’ – in such a scenario, how is encoding, processing and transmission performed with high reliability without error? 5) Given the sheer complexity of the number of neurons and their interconnections, how does such a highly complex, noisy network function 10 to yield (largely) consistent response and behavioural decisions from the organism? 6) How does memory play a role in all this? 9) Last and the most important – how does all this translate to the larger question of Mind and Consciousness?
The research teams in Neuroscience of today and tomorrow are made up of neurologists, electrical engineers and computer scientists, medical imaging researchers, physicists, psychiatrists, psychologists, neurosurgeons, mathematicians and philosophers (and not to forget animals and human volunteers for brain studies). Where Are We Today? Neuroscience has come a long way since the papyrus containing description of 48 cases related to the brain, written by an Egyptian surgeon thousands of years ago (an American Egyptologist named Edwin Smith first discovered this papyrus in 1862 AD). The Spanish Nobel laureate Santiago Cajal established the central tenet of modern neuroscience in 1889 – the ‘neuron doctrine’: that the nervous system is composed of discrete individual nerve cells which are independent elements (the term ‘neuron’ was coined by the German anatomist Wilhelm von Waldeyer in 1891 AD). Localism (the view that neurons and brain areas have specific functions) and holism (neurons work more as aggregate field) is now being replaced by “connectionism”. This view contends that lower level functions (primary sensory/motor functions) are strongly localized but higher-level functions (object recognition, memory, and language) are the result of interconnections 11 between different brain areas. In addition, even within areas that seem to be localized for a particular function, that function is found to be distributed among many neurons.