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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.

Abstract

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.

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Figure 1: Auditory imagery.
Figure 2: Mental rotation.
Figure 3: Area 17 is involved in visual imagery.

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MIT ENCYCLOPEDIA OF COGNITIVE SCIENCES

Imagery

Positron emission tomography

Magnetic resonance imaging

Single-neuron recording

Glossary

BEHAVIOURISM

The school of psychology that focused solely on observable stimuli, responses and the consequences of responses.

TRANSCRANIAL MAGNETIC STIMULATION

(TMS). A technique used to induce a transient interruption of normal activity in a relatively restricted area of the brain. It is based on the generation of a strong magnetic field near the area of interest, which, if changed rapidly enough, will induce an electric field sufficient to stimulate neurons.

MOTOR STRIP

Primary motor cortex (area M1). Part of the frontal lobe, which is used to control fine-grained movements.

SINGLE-PHOTON EMISSION COMPUTED TOMOGRAPHY

(SPECT). A method in which images are generated by using radionuclides that emit single photons of a given energy. Images are captured at multiple positions by rotating the sensor around the subject; the three-dimensional distribution of radionuclides is then used to reconstruct the images. SPECT can be used to observe biochemical and physiological processes, as well as the size and volume of structures.

HIGH-RESOLUTION DETAIL

A feature of a visual percept or image that requires high resolution (operationalized here as 0.5° of visual angle or less, as viewed from the subject's vantage point) to discern. A meta-analysis indicates that the early visual cortex is activated during visual mental imagery when the task requires the extraction of high-resolution details from a visualized stimulus.

RECEPTIVE FIELD

The area of the sensory space in which stimulus presentation leads to the response of a particular sensory neuron.

DIFFUSE OPTICAL TOMOGRAPHY

(DOT). A neuroimaging technique that uses arrays of lasers and detectors to measure changes in the absorption of near-infrared light caused by neural activation. The most widely used type of DOT measures changes in blood oxygenation caused by neural activity.

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Kosslyn, S., Ganis, G. & Thompson, W. Neural foundations of imagery. Nat Rev Neurosci 2, 635–642 (2001). https://doi.org/10.1038/35090055

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