CCNCS Seminar Details
A direct link between primary visual cortex functioning and iconic memory capacity
|Date/Time:||Wednesday 4 December 2013, 4.15pm|
|Location:||Woolf College W1-SR5|
While iconic memory has been studied for over 50 years, very little is know about its neural basis. In part, this is due to the difficulty of studying neural correlates of a memory storage that has brief lifetime (requiring fast neuroimaging techniques) and high capacity (requiring precise imaging methods). Here, we take a rather indirect approach to investigate the neural basis of iconic memory. In the first voxel-based morphometry (VBM) study, we investigated which neural structures correlated with iconic memory capacity and we observed that people with larger grey matter volume in the calcarine sulcus could report more information from iconic memory. In a second study employing magnetic resonance spectroscopy (MRS), we found that people with higher GLX concentration (glutamate/glutamine) in primary and secondary visual cortex seemed to have higher iconic memory capacity. As both these studies are correlational in nature, we aimed to confirm our findings in a causal way by manipulating GLX and GABA concentration in primary/secondary visual cortex. We did this by applying transcranial direct current stimulation (tDCS) over visual cortex with a reference electrode over motor cortex (see Stagg et al., 2009; anodal tDCS selectively lowers GABA, cathodal tDCS lowers GLX and GABA). Indeed, we observed significant modulations in iconic memory capacity after application of tDCS. Importantly, in all these studies no relation between visual working memory capacity and brain volume/neurotransmitter concentration in primary visual cortex was found. Altogether, these results show that there is a causal link between primary cortex functioning and iconic memory capacity.