Johns Hopkins School of Medicine

The hippocampus is a brain area involved in learning and memory.  The dentate gyrus, a subregion of the hippocampus, may prevent interference between similar memories, but it is unclear how the two main dentate gyrus cell types, granule cells and mossy cells, contribute to this process.  GoodSmith et al. recorded from granule cells and mossy cells as rats explored distinct environments.  Different groups of granule cells fired in different environments, but mossy cells fired in multiple locations in most environments, a feature previously attributed to granule cells. This study resolves a longstanding debate about the firing properties of granule cells, shows that mossy cells have spatial firing, and describes distinct ways in which granule cells and mossy cells can contribute to the ability to distinguish between environments.

Mind Brain Institute (MBI) graduate student Doug GoodSmith and postdoctoral fellow Xiaojing Chen published a new paper in Neuron. This paper resulted from a collaboration between the Knierim lab of MBI and Kim Christian of the Song lab of the JHU Institute for Cell Engineering.  Their findings described the spatial firing characteristics and pattern separation properties of different cell types in the dentate gyrus region of the hippocampus. 

GoodSmith D, Chen X, Wang C, Kim SH, Song H, Burgalossi A, Christian K, and Knierim JJ.  Spatial Representations of Granule Cells and Mossy Cells of the Dentate Gyrus.

Neuron 93:677-90, 2017.

http://www.cell.com/neuron/fulltext/S0896-6273(16)30999-0

See Preview in Neuron:

Nakazawa K. Dentate Mossy Cell and Pattern Separation. Neuron 93:465-7, 2017.

http://www.cell.com/neuron/fulltext/S0896-6273(17)30045-4

Excerpt: GoodSmith et al. (2017) identified rat granule cells and CA3 pyramidal cells based on detailed histological identification of the position of recording electrodes, showing these two cell types tend to have a single firing field in a single environment. In contrast, mossy cells in the hilus tended to have multiple firing fields and to fire in multiple different environments. They reported that only 9% of granule cells are active in a given environment, compared to 29% of CA3 neurons and 88% of mossy cells. Impressively, they also back up their data with juxtacellular recording of a small number of granule cells and hilar mossy cells for morphological identification, allowing them to confirm the very sparse firing of granule cells compared to mossy cells.