On imputing function to structure from the behavioural effects of brain lesions

What is the link, if any, between the patterns of connections in the brain and the behavioural effects of localized brain lesions. We explored this qu estion in four related ways. First, we investigated the distribution of act ivity decrements that followed simulated damage to elements of the thalamoc ortical network, using integrative mechanisms that have recently been used to successfully relate connection data to information on the spread of acti vation, and to account simultaneously for a variety of lesion effects. Seco nd, we examined the consequences of the patterns of decrement seen in the s imulation for each type of inference that has been employed to impute funct ion to structure on the basis of the effects of brain lesions. Every variet y of conventional inference, including double dissociation, readily misattr ibuted function to structure. Third, we tried to derive a more reliable fra mework of inference for imputing function to structure, by clarifying conce pts of function, and exploring a more formal framework, in which knowledge of connectivity is necessary but insufficient, based on concepts capable of mathematical specification. Fourth, we applied this framework to inference s about function relating to a simple network that reproduces intact, lesio ned and paradoxically restored orientating behaviour. Lesion effects could be used to recover detailed and reliable information on which structures co ntributed to particular functions in this simple network. Finally, we explo red how the effects of brain lesions and this formal approach could be used in conjunction with information from multiple neuroscience methodologies t o develop a practical and reliable approach to inferring the functional rol es of brain structures.