Inputs to the brain from sensors alter the activities of particular neurones. They also alter the "brain state". But the ability of the sensors to deliver information to the brain depends on the brain state. An obvious example is the difference between a sleeping person and an alert one. Also, "control" neurones can alter the responses of the sensors. Processes similar to lateral inhibition can enable particular pathways in the brain to facilitate or inhibit specific sensory inputs.
In short, we can summarise the brain's activities by a diagram similar to the one that summarised our characterisation of the living state (chapter 10).
This diagram could be taken to characterise the mind of any animal capable of intelligent behaviour, as defined in chapter 16. At any moment, stimuli from the body and from the surroundings are activating sensors, so information is being sent to the brain. Which sensory information is processed depends on the brain state as a whole (whether the animal is alert and attentive to particular inputs) and on the activities of groups of neurones that affect signal processing pathways. The brain state changes from moment to moment, according to current and recent sensory inputs and to the activities of individual neurones and circuits of neurones.
We suggest that mind describes the interdependences among brain state, sensory inputs and neuronal activity patterns at any instant, and the continuity of these interdependences. In humans, with their capacity for abstraction and language, mind can express itself. Hence the much-discussed features of mind that do not appear at first sight to be features of the brain: consciousness or self-awareness, subjectivity and intentionality. ("Intentionality" is a philosophical term, meaning that our thoughts are always "about" something.) As we suggested at the end of chapter 17, there is nothing mystical or non-biological about these features of mind - and nor are they empty words. They are meaningful, but they are accessible to biological (specifically neurobiological) understanding.
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