Study explores neural signals in memory formation

How does the brain form new memories? A recent study has challenged the long held view that enhanced synchronisation in the medial temporal lobes is positively related to energy consumption.

Converging evidence shows that the key brain structures crucial for the formation of new memories are located in the medial temporal lobes (MTL). The same MTL regions are not only essential for memory, but these regions are also involved in spatial processing and navigation. This understanding of the relationship between memory encoding and spatial processing is well established. The beneficial effect of spatial processing on memory encoding has been known since ancient Greek times, when the Method of Loci, a mnemonic using spatial processing to enhance memory was first described. Items to be remembered using this mnemonic are imagined along a familiar path, for example, the items of a grocery shopping are imagined along one´s daily commute.  In the supermarket all items of the shopping list can then be easily retrieved by imagining the path again. To this day memory athletes use the Method of Loci to memorise impressive amounts of seemingly arbitrary information.

For the last two decades the neural signature of the medial temporal lobe was assumed to be (i) an increase in energy consumption (i.e. BOLD), and (ii) increased synchronisation at a frequency at around 4-7 Hz. However, occasionally decreased synchronisation related to memory has been reported, raising the question of how the two neural signals are really related in this region. In a recent study, led by Dr Marie-Chrisin Fellner and Dr Simon Hanslmayr, the authors demonstrate that desynchronisation in the 4-7 Hz frequency in the medial temporal lobe co-occur with enhanced energy consumption in this same region. This effect was most pronounced when participants engaged in an encoding strategy, the so-called ‘method of loci’, that leads to extraordinarily good memory performance. These findings are surprising in that they challenge the long held view that enhanced synchronisation in the MTL is positively related to energy consumption.   

Reference
Fellner, M.-C., Volberg, G., Wimber, M., Goldhacker, M., Greenlee, M. W., & Hanslmayr, S. (2016). Spatial Mnemonic Encoding: Theta Power Decreases and Medial Temporal Lobe BOLD Increases Co-Occur during the Usage of the Method of Loci. ENEURO, 3(6) e0184-16.2016 1–16