Covert cognition in the persistent vegetative state.

Brain damage can sometimes render a patient persistently unresponsive and yet apparently awake, admitting the possibility that the absence of overt voluntary behaviour might conceal a retained capacity for covert cognition. When given instructions to perform a cognitive task, a minority of patients in such a so-called persistent vegetative state (PVS) has recently been found to exhibit patterns of brain activation closely matching those observed in normal subjects obeying the same instructions. These data have been widely interpreted as implying the detection of covert "consciousness". Here we show that this inference is not supported by the extant data because it relies on critical assumptions, obscured by conceptual unclarities, that are either untested or untestable. We set out the proper grounds for ascribing psychological attributes to PVS patients from physiological evidence of any kind, and offer a perspicuous conceptual framework for future empirical studies in the field.

Language and cortical function: conceptual developments.

Mastery of a language is a capacity that distinguishes humans from other animals. Attempts to identify the brain functions that are necessary for the possession of linguistic skills began in the 19th century with the research of Broca and Wernicke. We trace the principal experimental developments since then, ranging from psychological studies of aphasic patients to non-invasive brain-imaging investigations. The development of theories concerning word recognition, reading aloud, fluent speech and understanding utterances are described. Possible brain regions involved in these abilities, identified by means of non-invasive imaging, are considered. We examine the various claims made by these researchers as to what their experiments show and in particular examine the validity of their theories. This conceptual analysis shows that in many cases the interpretation of experiments is confused and that the theories elaborated are not tenable. We seek to clarify what can be substantiated concerning the workings of the brain and the exercise of linguistic skills.

Emotion and cortical-subcortical function: conceptual developments.

Biologists have studied the expression of emotions in man and other animals since at least 1806, when Charles Bell published his Anatomy and Physiology of Expression. We trace the main experimental developments since that time, including Darwin's investigations into the evolution of innate forms of expression of emotions, as well as those into cognitive versus precognitive forms of expression of emotions. In particular, contemporary studies by neuroscientists into the origins of emotional experiences are detailed, especially emotional responses to faces showing different expressions, on which much research has been carried out. We examine the various claims made by these researchers as to what their experiments show. Our conceptual analysis indicates that there is considerable confusion as to what experimental work to this time indicates about the role of cortical and subcortical structures in the expression of emotions. We attempt to clarify what can and cannot be justified as established concerning the workings of the brain and emotions.

The motor system in neuroscience: a history and analysis of conceptual developments.

Neuroscientific reflection on the integrative action of the nervous system was dominated by consideration of the motor system from the time of Aristotle in the 4th century B.C. to that of Sherrington, his contemporaries and proteges in the first-half of the 20th century. We describe the significant discoveries concerning the action of the spinal cord and cortex in motor phenomena during this period. This provides a vivid account of how great neuroscientists, over a period of more than 2000 years, have endeavoured to clarify notions concerning the integrative action of the nervous system in the context of the prevailing philosophical traditions of their times. We examine these traditions as well as the conceptual schemes offered by neuroscientists, especially in relation to the workings of the cortex. It is shown that neuroscientists cleave to this day to a tradition that goes back to Descartes, and that this is the case even for those who explicitly claim to reject such a tradition. The review concludes with what we take to be an appropriate basis for rejecting the Cartesian paradigm that we hope will assist neuroscientists in understanding the integrative action of the nervous system.