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Julie Golomb, Barbara Ruf, Jenika Beck, Aybala Saricicek, Jian Hu, Marvin Chun, Zubin Bhagwagar; Diminished center-surround inhibition in patients with a history of depression. Journal of Vision 2008;8(6):1029. doi: 10.1167/8.6.1029.
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Center-surround antagonism is one of the most fundamental properties of the visual system and is thought to rely on interactions involving the neurotransmitter GABA. The perceptual consequences of this antagonism have been demonstrated in psychophysical studies of visual motion processing (Tadin et al., Nature 2003). Increasing the size of a low contrast stimulus will increase its discriminability due to spatial summation. Increasing the size of a high contrast stimulus, however, results in spatial suppression, and behavioral performance is impaired. Interestingly, this spatial suppression is not exhibited in older adults, presumably because of decreased GABAergic interactions (Betts et al., Neuron 2005). Using a visual motion processing paradigm, we tested whether surround inhibition is similarly diminished in medication-free patients with a history of recurrent unipolar depression, a disorder which has been linked to reduced levels of occipital GABA (Bhagwagar et al., Biol Psych 2007). Participants viewed drifting gratings of either low (2.8%) or high (92%) contrast and small (0.7 deg) or large (5.0 deg) size. The task was a two-alternative forced choice discriminating between leftward and rightward direction of motion. The duration of each exposure was stair-cased to obtain the threshold duration for each of the four conditions. Both healthy control and recovered depressed participants exhibited comparable amounts of summation for the low contrast stimuli. However, the patient population showed significantly reduced spatial suppression for the high contrast stimuli compared to the age-matched controls. This suggests that decreased GABA levels associated with depression may have ubiquitous and persistent consequences, even for basic sensory processing.
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