Thalamus and Vision

The Thalamus and Vision

The Thalamic Involvement in Vision

Aside from Bruce Willis starring movies such as The Sixth Sense, humans are generally believed to have five senses: vision, hearing, touch, smell and taste. In neuroscience, these are subdivided into the sensation, perception and interpretation stages. Thus, vision would first be acknowledged by receptors (rods and cones in the retina at the back of the eye), then transmitted to the brain’s “relay station” — the thalamus, and finally processed in the visual cortex in the occipital lobe.

Further, the thalamus is composed of three elements: the lateral geniculate nucleus, the pulvinar and the thalamic reticular nucleus. Moreover, thalamic neurons come in three types: magnocellular, parvocellular and koniocellular; each contributuing diversely to visual input processing and connecting to dissimilar layers of the visual cortex.

Saalmann & Kastner (2009) explain that there is agreement in the literature that the thalamus relays sensory signals to the brain. However, in their account, the researchers demonstrate that the real picture is much more complicated, engaging the contribution of the pulvinar and geniculate nucleus, and awarding greater control to the structure over vision in general.

When objects move too quickly, they are seen as blurry. Fantasy art girl. Image: Megan Jorgensen (Elena)

Rees (2009) adds credence to the above affirmation, reiterating that evidence is growing that the thalamus is more active in directing the specific perceptive ability. So, it may be that thalamic nuclei determine where observatory attention is allocated.

Whether the role played by the brain region of interest in this brief essay is primary or secondary in administering this particular human sense, fMRI, electrophysiological and histological data are continuing to shed light on the subject. For a more detailed mapping of the brain area, one is referred to Krauth et al. (2010).

References:

• Krauth, A., Blanc, R., Poveda, A., Jeanmonond, D., Morel, A. and Szekely, G. (2010). A mean three-dimensional atlas of the human thalamus: Generation from multiple histological data. NeuroImage, 69: 2053-62.
• Rees, G. (2009). Visual attention: The thalamus at the centre? Current Biology, 19 (5): R213-4.
• Saalmann, Y. B & Kastner, S. (2009). Gain control in the visual thalamus during perception and cognition. Current
• Opinion in Neurobiology, 662 (19): 1-7.[Article in Press; available online at http://www.princeton.edu/~napl/pdf/Saalmann_Kastner_09.pdf ]

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