As seen in part II, some neurons have receptive fields. The receptive field of a neuron corresponds to the portion of the screen where a stimulus should appear in order to elicit a response from that neuron. That portion of the screen represents the world that the neuron sees.
Evidence for predictive shifts
The predictive shifts of receptive fields has been first demonstrated in the lateral intraparietal area (LIP) by Duhamel, Colby and Goldberg (1992). In LIP, the receptive field location is defined in retinocentric coordinates, i.e. it is fixed with respect to the fovea (i.e. the center of the retina). If a stimulus is flashed in the receptive field of a LIP neuron, the neuron responds after a delay of 70ms.
This feature is not restricted to LIP but pertains to most of the visual system areas (frontal eye fields - FEF, extravisual cortex, ...)
Predictive shifts of receptive fields preserves visual stability
Saccades are very fast process that changes our perception of the world in a few tens of milliseconds. Without any compensation, the whole visual world would appear to jump during each saccade as the retinal position of all the objects present in the visual environment is shifted during each saccade. A predictive shift of receptive allows the maintenance of visual stability.
Let's consider the following example: If you fixate the area A of the image below and then the area B, the immediate surrounding of the fixation point will dramatically change during the saccade.
Predictive shifts of receptive fields is elicited by efference copy
Each time an eye movement is executed, the motor areas of the oculomotor system (e.g. the superior colliculus) send a signal to the eye muscles in order to make the eye moving. In parallel, a copy of this signal (called either efference copy or corollary discharge) is fed back to brain areas that are involved in vision and eye movements. This efference copy signal is thought to be responsible for the predictive shift in receptive fields. In a series of paper, Marc Sommer and Robert Wurtz determine that a copy of the motor commands sent to the eye muscles by the superior colliculus (SC), was also conveyed to the frontal eye fields (FEF) via the thalamus (Sommer and Wurtz 2002). In addition, they demonstrated that this corollary discharge signal was necessary for predictive shift in receptive fields as inactivation of the thalamus also impairs the predictive shift of FEF neurons during saccadic eye movements (Sommer and Wurtz 2006).
In conclusion, taking into account the future consequence of our future eye movements helps maintaining the stability of our visual environment. The manifestation of this prediction resides in the predictive shift of receptive fields in visual areas. Predicting the future consequence of our movements will be a key aspect of the predictive control of arm movement, which will be the topic of a future post.
Talk by M. Sommer: http://www.pratt.duke.edu/lecture/sommer
Talk bu R. Wurtz: http://videocast.nih.gov/launch.asp?12695
Duhamel, J., Colby, C. L., & Goldberg, M. E. (1992). The updating of the representation of visual space in parietal cortex by intended eye movements. Science, 255(5040), 90-2.
Sommer, M. A., & Wurtz, R. H. (2002). A pathway in primate brain for internal monitoring of movements. Science (New York, N.Y.), 296(5572), 1480-2. doi: 10.1126/science.1069590.
Sommer, M. A., & Wurtz, R. H. (2006). Influence of the thalamus on spatial visual processing in frontal cortex. Nature, 444(7117), 374-7. doi: 10.1038/nature05279.
Sommer, M. A., & Wurtz, R. H. (2008). Brain circuits for the internal monitoring of movements. Annual review of neuroscience, 31, 317-38. doi: 10.1146/annurev.neuro.31.060407.125627.