Two new papers published!

Two of our papers came out during the last few weeks. In “Population code in mouse V1 facilitates read-out of natural scenes through increased sparseness” (published in Nature Neuroscience), we show that higher order correlations in natural scenes lead to increased population sparseness, improving the representation of natural scenes in the population code. In “State dependence of noise correlations in macaque V1” (published in Neuron), we show that global activity fluctuations in neural activity lead to noise correlations during anesthesia, and that removing these global fluctuations recovers the awake correlation structure.

New review by Maoz Shamir on the “Emerging principles of population coding: in search for the neural code”

shamir

A new review on population coding by Maoz Shamir is appearing in the April issue of Current Opinion in Neurobiology. Shamir discusses how correlated noise negatively impacts neural coding, when the noise overlaps with the signal, and how this effect can be overcome by introducing heterogeneity into the population model.  Importantly, he points out that current population coding models are heavily underconstraint, such that additional assumptions are needed for testing them. The review references much of our work on population coding over the past 5 years or so, which was nice to see. Overall, this very interesting special issue on theoretical and computational neuroscience assembled by Adrienne Fairhall and Haim Sompolinsky is highly recommended

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Calling R from Matlab

I do most of my programming and data analysis in Matlab (still and despite all the issues with licensing and so). But quite a few statistical methods come as nice packages for R and are not available for Matlab, or only in poor quality. I recently encountered such a case again and went to search for a solution that lets you call R-code from Matlab. I looked around a bit and decided on the option described on Rwiki. Basically, you use saveR to save your Matlab variables so that R can read them, you run a R script using the ! operator in Matlab, which saves its output using the R.matlab package. Then you load the results in Matlab. I just started with the demo scripts and modified them for my own needs. Works beautifully! 

Orientation preference of LFP gamma activity

When we originally submitted our 2008 paper on the orientation selectivity of LFP gamma band activity, the response of one of the reviewers was: “It simply reeks of artefact.” We had found that the LFP gamma band power across our whole array of tetrodes spanning ~1 mm was tuned to the same orientation (give and take) and the preferred orientations hardly correlated with that of the multi unit activity. But after going through many rounds of analysis, I was convinced that our finding was correct and we eventually published the paper.

Nevertheless, I was quite relieved when another group independently obtained the same result: Jia, Smith and Kohn reported in their 2011 paper that for large stimuli (as also used in our study), all LFP sites in an array spanning ~4 mm show the same preferred orientation. In addition, they verified this finding independently with single electrodes and still obtained the same results. Interestingly, they found that when using smaller stimuli, LFP sites exhibit different orientation preferences which correlate well with the multi-unit orientation preference at the site.

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