Neural foundations of imagery

Key Points Recent advances in cognitive neuroscience, including functional brain-imaging techniques, have shown that mental imagery makes use of much the same neural substrates as perception in the same sensory modality. Visual mental imagery seems to use the same two pathways (ventral or object processing, and dorsal or spatial processing) as perception. Defects in one or other pathway often, but not always, produce parallel deficits in both perception and imagery. Auditory and motor imagery also draw on cortical areas involved in auditory perception and motor control, respectively. There is evidence that early visual cortex (areas 17 and 18) is activated during some types of mental imagery. Detection of such activity seems to rely on the use of the most sensitive imaging techniques. It is possible that these areas are activated only if the imagery task used requires subjects to find high-resolution detail in a mental image. Imagery of emotional events can activate the autonomic nervous system and amygdala in a similar way to perception of the same events, leading to physiological changes. For example, imagining threatening events can increase heart rate, skin conductance and breathing rate. Future research should clarify the involvement of primary sensory cortices in imagery, and investigate individual variation in imagery abilities, among other issues. New imaging techniques, such as functional diffuse optical tomography, will aid these advances. Mental imagery has, until recently, fallen within the purview of philosophy and cognitive psychology. Both enterprises have raised important questions about imagery, but have not made substantial progress in answering them. With the advent of cognitive neuroscience, these questions have become empirically tractable. Neuroimaging studies, combined with other methods (such as studies of brain-damaged patients and of the effects of transcranial magnetic stimulation), are revealing the ways in which imagery draws on mechanisms used in other activities, such as perception and motor control. Because of its close relation to these basic processes, imagery is now becoming one of the best understood 'higher' cognitive functions.