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Archive for October, 2008

The recent issue of the journal Hippocampus has an interesting article on the structure of the hippocampus throughout the menstrual cycle. By studying women two times during the menstrual cycle (pre- and post-menstrual) using volumetric MR scanning, researchers Xenia Protopopescu and her colleagues at Cornell University demonstrated structural changes in the hippocampus. Specifically, gray matter was relatively increased in the right anterior hippocampus and relatively decreased in the right dorsal basal ganglia (globus pallidus/putamen) in the postmenstrual phase.

Below is an image from that article, showing a t-map rendering showing increased anterior hippocampus (yellow) and decreased basal ganglia (pink) in the postmenstrual vs. premenstrual phase. Seems to me that the entorhinal cortex was also affected

Correspondingly, verbal declarative memory changed throughout the cycle: memory performance increased in teh postmenstrual vs. premenstrual phase. These results support models of estrogen-dependent cyclical alterations in hippocampal synaptic density and function proposed to account for neuronal and cognitive differences seen across the menstrual cycle.

The basal ganglia findings were rather unexpected, and the researchers suggest that:

(…) estrogens have been shown to increase striatal dopamine release, to influence striatal serotonergic and dopaminergic innervation density, and to promote striatal medium size spiny neuronal maturation in vivo (Korol, 2004b). The apparent opposite effect of high estrogen levels on hippocampal and basal ganglia gray matter may relate to the finding in rats that high estrogen promotes use of a hippocampally-mediated spatial (place or allocentric) learning strategy, while low levels promote use of a nonhippocampal, possibly striatally-mediated navigational (response or egocentric) strategy (Korol, 2004b). In humans, MRI studies have shown that navigational ability correlates with level of activity in the basal ganglia (putamen) (Epstein et al., 2005), and more specifically, that navigation using a response strategy is associated both with greater activity (Iaria et al., 2003) and gray matter (Bohbot et al., 2007) in the basal ganglia (caudate), though it should be noted that menstrual cycle effects were not assessed in any of these studies.

I can imagine the jokes that may come out of this… but leave it for now 😀 One thing that strikes me is the question of how these changes are related to the menopause. For example, would these changes mean that intra-individual variation during the month would be reduced after the menopause? As one knows from ageing research, such variance increases with age. So it is even conceiveable that the development goes the opposite way.

I also notice that the same researchers have recently demonstrated a link between changes in orbitofrontal cortex and emotional processing. It’s also worth a read.

-Thomas

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In case any of you have plans for going to the first NeuroPsychoEconomics conference in Munich this Thursday and Friday, let me know. Or if you’re just in the vicinity, you can also let me know. Neuroethicists and cognitive neuroscientists alike (as well as every else interested in this blog) should probably meet whenever possible.

The plan is to give a talk entitled something like “Individual biological differences and models of value-based decision making” (PDF). which hopefully will also soon be out as an article. Comments are of couse welcome. Here is the abstract teaser:

Neuroeconomics is the scientific, multidisciplinary study of value-based decision making. Recent advances in methods and findings in cognitive neuroscience have gained attention and influence on our understanding of the basic mechanisms of behaviour. With the advent of two new paradigms in cognitive neuroscience – imaging genetics and the cognitive neuroscience of ageing – the focus of brain-behaviour research is turning towards the study of normal variation and individual differences. As such, insights from these approaches hold the promise to provide a more detailed account of value-based decision making. In addition, this understanding may provide the means to induce short-term and reversible alterations in decision behaviours. In this paper, we present and discuss these insights and how they may inform the neuroeconomic study of decision making.

-Thomas

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Current Opinion in Neurobiology now hosts a wonderful special issue on “Cognitive Neuroscience”. Well, it’s actually more narrow and to the point than this. Many of the articles are about the neurobiology of preference formation and decision making. The following articles are included:

Dissociating explicit timing from temporal expectation with fMRI
by JT Coull, AC Nobre

The neurobiology of social decision-making
by James K Rilling, Brooks King-Casas, Alan G Sanfey

Anchors, scales and the relative coding of value in the brain
by Ben Seymour, Samuel M McClure

Reinforcement learning: The Good, The Bad and The Ugly
by Peter Dayan, Yael Niv

Axiomatic methods, dopamine and reward prediction error
by Andrew Caplin, Mark Dean

New insights on the subcortical representation of reward
Okihide Hikosaka, Ethan Bromberg-Martin, Simon Hong, Masayuki Matsumoto

From biophysics to cognition: reward-dependent adaptive choice behavior
by Alireza Soltani, Xiao-Jing Wang

Spiking networks for Bayesian inference and choice
by Wei Ji Ma, Jeffrey M Beck, Alexandre Pouget

No doubt: if you read these articles, you will be very much up to date with the latest developments in decision neuroscience, neuromarketing, or whatever you wish to call it. Although these articles are not explicitly part of a special issue dedicated to this theme, they nevertheless could be read as such. A wonderful update from a journal that rarely makes the headlines but deserves all the attention it can get.

-Thomas

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