We have a new paper which explores the spatial functions of the rostral thalamus, a complex group of thalamic nuclei. Here, we concentrate on analysing the functions of three of these nuclei (the anteromedial nucleus, the parataenial nucleus and nucleus reuniens). We show that there are place cells, head direction cells, and border/perimeter cells present in these nuclei.
Evidence for Spatially-Responsive Neurons in the Rostral Thalamus
MM Jankowski, Johannes Passecker, Md Nurul Islam, Seralynne Vann, Jonathan T. Erichsen, JP Aggleton, and Shane M. O‘Mara
Damage involving the anterior thalamic and adjacent rostral thalamic nuclei may result in a severe anterograde amnesia, similar to the amnesia resulting from damage to the hippocampal formation. Little is known, however, about the information represented in these nuclei. To redress this deficit, we recorded units in three rostral thalamic nuclei in freely-moving rats (the parataenial nucleus, the anteromedial nucleus and nucleus reuniens). We found units in these nuclei possessing previously unsuspected spatial properties. The various cell types show clear similarities to place cells, head direction cells, and perimeter/border cells described in hippocampal and parahippocampal regions. Based on their connectivity, it had been predicted that the anterior thalamic nuclei process information with high spatial and temporal resolution while the midline nuclei have more diffuse roles in attention and arousal. Our current findings strongly support the first prediction but directly challenge or substantially moderate the second prediction. The rostral thalamic spatial cells described here may reflect direct hippocampal/parahippocampal inputs, a striking finding of itself, given the relative lack of place cells in other sites receiving direct hippocampal formation inputs. Alternatively, they may provide elemental thalamic spatial inputs to assist hippocampal spatial computations. Finally, they could represent a parallel spatial system in the brain.
Place cells are present in the parataenial, anteromedial, and nucleus reuniens of the thalamus, and are not topographically-organised:
Cells exhibiting the characteristic phenotype that passes threshold for classical hippocampal place cells were found in PT, AM and NRe .
Cells recorded in PT and AM had relatively sharp and small place fields, compared to cells recorded in NRe (the maps show raw spiking activity superimposed on the path of the animal, firing intensity maps and on place field maps).
NRe cells were characterized by generally higher spontaneous activity outside the center of the place field and thus wider receptive fields. Place cells found in NRe had significantly lower spatial information content than those from PT or AM.
Place cells recorded in PT and AM sometimes formed two or three place fields, unlike NRe cells which usually fired mainly at single somewhat less precisely-defined location.
The activity of the majority of cells from all three nuclei was entrained by 6-12 Hz oscillations as depicted on ±1000 ms autocorrelograms (i.e. theta frequency).
However, the firing activity of some units in NRe did not show any rhythmicity.
All place cells show sharply-defined, location-specific firing that remains stable and constant across the duration of the recording session.
The recorded place cells do not appear to exhibit a topographic organisation because simultaneously-recorded cells (e.g. on Figure see pairs of cells 5 and 13 or 11 and 12 recorded simultaneously in anteromedial nucleus or cells 2 and 3 recorded simultaneously in parataenial nucleus) all show place fields that are distal to each other within the recording arena.