Raising the profile of the anterior thalamus

1999 ◽  
Vol 22 (3) ◽  
pp. 447-448 ◽  
Author(s):  
John C. Dalrymple-Alford ◽  
Anna M. Gifkins ◽  
Michael A. Christie
Keyword(s):  
Perirhinal Cortex ◽  
Thalamic Nuclei ◽  
Anterior Thalamus ◽  
Target Article ◽  
Anterior Thalamic Nuclei

Three questions arising from Aggleton & Brown's target article are addressed. (1) Is there any benefit to considering the effects of partial lesions of the anterior thalamic nuclei (AT)? (2) Do the AT have a separate role in the proposed extended hippocampal system? (3) Should perirhinal cortex function be restricted to familiarity judgements?

scholarly journals Anterior thalamic nuclei neurons sustain memory

2021 ◽  
Author(s):  
S. C. Barnett ◽  
L.C. Parr-Brownlie ◽  
B. A. L. Perry ◽  
C. K. Young ◽  
H. E. Wicky ◽  
...  
Keyword(s):  
Working Memory ◽  
Electrical Activity ◽  
Spatial Working Memory ◽  
Memory Function ◽  
Memory System ◽  
Mammillary Body ◽  
Thalamic Nuclei ◽  
Anterior Thalamus ◽  
Anterior Thalamic Nuclei ◽  
Mammillothalamic Tract

AbstractA hippocampal-diencephalic-cortical network supports memory function. The anterior thalamic nuclei (ATN) form a key anatomical hub within this system. Consistent with this, injury to the mammillary body-ATN axis is associated with examples of clinical amnesia. However, there is only limited and indirect support that the output of ATN neurons actively enhances memory. Here, in rats, we first showed that mammillothalamic tract (MTT) lesions caused a persistent impairment in spatial working memory. MTT lesions also reduced rhythmic electrical activity across the memory system. Next, we introduced 8.5 Hz optogenetic theta-burst stimulation of the ATN glutamatergic neurons. The exogenously-triggered, regular pattern of stimulation produced an acute and substantial improvement of spatial working memory in rats with MTT lesions and enhanced rhythmic electrical activity. Neither behaviour nor rhythmic activity was affected by endogenous stimulation derived from the dorsal hippocampus. Analysis of immediate early gene activity, after the rats foraged for food in an open field, showed that exogenously-triggered ATN stimulation also increased Zif268 expression across memory-related structures. These findings provide clear evidence that increased ATN neuronal activity supports memory. They suggest that ATN-focused gene therapy may be feasible to counter clinical amnesia associated with dysfunction in the mammillary body-ATN axis.HighlightsThe mammillothalamic tract (MTT) supports neural activity in an extended memory system.Optogenetic activation of neurons in the anterior thalamus acutely improves memory after MTT lesions.Rescued memory associates with system-wide neuronal activation and enhanced EEG.Anterior thalamus actively sustains memory and is a feasible therapeutic target.Abstract FigureOptostimulation of anterior thalamus restores memory function after MTT lesionsCreated with BioRender.com

scholarly journals Thanks for the memories: Extending the hippocampal-diencephalic mnemonic system

1999 ◽  
Vol 22 (3) ◽  
pp. 471-479 ◽  
Author(s):  
John P. Aggleton ◽  
Malcolm W. Brown
Keyword(s):  
Prefrontal Cortex ◽  
Recognition Memory ◽  
Episodic Memory ◽  
Temporal Lobe ◽  
Thalamic Nuclei ◽  
Target Article ◽  
Anterior Thalamic Nuclei ◽  
Relationship Of ◽  
The Relationship ◽  
Key Questions

The goal of our target article was to review a number of emerging facts about the effects of limbic damage on memory in humans and animals, and about divisions within recognition memory in humans. We then argued that this information can be synthesized to produce a new view of the substrates of episodic memory. The key pathway in this system is from the hippocampus to the anterior thalamic nuclei. There seems to be a general agreement that the importance of this pathway has previously been underestimated and that it warrants further study. At the same time, a number of key questions remain. These concern the relationship of this system to another temporal-lobe/diencephalic system that contributes to recognition, and the relationship of these systems to prefrontal cortex activity.

scholarly journals Trajectory of hippocampal fibres to the contralateral anterior thalamus and mammillary bodies in rats, mice, and macaque monkeys

2019 ◽  
Vol 3 ◽  
pp. 239821281987120 ◽  
Author(s):  
Mathias L. Mathiasen ◽  
Rebecca C. Louch ◽  
Andrew D. Nelson ◽  
Christopher M. Dillingham ◽  
John P. Aggleton
Keyword(s):  
Thalamic Nucleus ◽  
Hippocampal Formation ◽  
Internal Capsule ◽  
Macaque Monkey ◽  
Head Direction ◽  
Thalamic Nuclei ◽  
Tracer Injection ◽  
Mammillary Bodies ◽  
Anterior Thalamus ◽  
Anterior Thalamic Nuclei

The routes by which the hippocampal formation projects bilaterally to the anterior thalamic nuclei and mammillary bodies were examined in the mouse, rat, and macaque monkey. Despite using different methods and different species, the principal pattern remained the same. For both target areas, the contralateral hippocampal (subiculum) projections arose via efferents in the postcommissural fornix ipsilateral to the tracer injection, which then crossed hemispheres both in or just prior to reaching the target site within the thalamus or hypothalamus. Precommissural fornix fibres could not be followed to the target areas. There was scant evidence that the ventral hippocampal commissure or decussating fornix fibres contribute to these crossed subiculum projections. Meanwhile, a small minority of postsubiculum projections in the mouse were seen to cross in the descending fornix at the level of the caudal septum to join the contralateral postcommissural fornix before reaching the anterior thalamus and lateral mammillary nucleus on that side. Although the rodent anterior thalamic nuclei also receive nonfornical inputs from the subiculum and postsubiculum via the ipsilateral internal capsule, few, if any, of these projections cross the midline. It was also apparent that nuclei within the head direction system (anterodorsal thalamic nucleus, laterodorsal thalamic nucleus, and lateral mammillary nucleus) receive far fewer crossed hippocampal inputs than the other anterior thalamic or mammillary nuclei. The present findings increase our understanding of the fornix and its component pathways while also informing disconnection analyses involving the hippocampal formation and diencephalon.

scholarly journals Multiplexed code of navigation variables in anterior limbic areas

2019 ◽  
Author(s):  
Jean Laurens ◽  
Amada Abrego ◽  
Henry Cham ◽  
Briana Popeney ◽  
Yan Yu ◽  
...  
Keyword(s):  
Navigation System ◽  
Neural Coding ◽  
Hippocampal Neurons ◽  
Large Fraction ◽  
Retrosplenial Cortex ◽  
Field Analysis ◽  
Head Direction ◽  
Thalamic Nuclei ◽  
Anterior Thalamus ◽  
Anterior Thalamic Nuclei

AbstractThe brain’s navigation system integrates multimodal cues to create a sense of position and orientation. Here we used a multimodal model to systematically assess how neurons in the anterior thalamic nuclei, retrosplenial cortex and anterior hippocampus of mice, as well as in the cingulum fiber bundle and the white matter regions surrounding the hippocampus, encode an array of navigational variables when animals forage in a circular arena. In addition to coding head direction, we found that some thalamic cells encode the animal’s allocentric position, similar to place cells. We also found that a large fraction of retrosplenial neurons, as well as some hippocampal neurons, encode the egocentric position of the arena’s boundary. We compared the multimodal model to traditional methods of head direction tuning and place field analysis, and found that the latter were inapplicable to multimodal regions such as the anterior thalamus and retrosplenial cortex. Our results draw a new picture of the signals carried and outputted by the anterior thalamus and retrosplenial cortex, offer new insights on navigational variables represented in the hippocampus and its vicinity, and emphasize the importance of using multimodal models to investigate neural coding throughout the navigation system.

scholarly journals Hippocampal–diencephalic–cingulate networks for memory and emotion: An anatomical guide

2017 ◽  
Vol 1 ◽  
pp. 239821281772344 ◽  
Author(s):  
Emma J. Bubb ◽  
Lisa Kinnavane ◽  
John P. Aggleton
Keyword(s):  
Prefrontal Cortex ◽  
Medial Temporal Lobe ◽  
Current Knowledge ◽  
Hippocampal Formation ◽  
Retrosplenial Cortex ◽  
Thalamic Nuclei ◽  
Mammillary Bodies ◽  
Individual Site ◽  
Multi Stage ◽  
Anterior Thalamic Nuclei

This review brings together current knowledge from tract tracing studies to update and reconsider those limbic connections initially highlighted by Papez for their presumed role in emotion. These connections link hippocampal and parahippocampal regions with the mammillary bodies, the anterior thalamic nuclei, and the cingulate gyrus, all structures now strongly implicated in memory functions. An additional goal of this review is to describe the routes taken by the various connections within this network. The original descriptions of these limbic connections saw their interconnecting pathways forming a serial circuit that began and finished in the hippocampal formation. It is now clear that with the exception of the mammillary bodies, these various sites are multiply interconnected with each other, including many reciprocal connections. In addition, these same connections are topographically organised, creating further subsystems. This complex pattern of connectivity helps explain the difficulty of interpreting the functional outcome of damage to any individual site within the network. For these same reasons, Papez’s initial concept of a loop beginning and ending in the hippocampal formation needs to be seen as a much more complex system of hippocampal–diencephalic–cingulate connections. The functions of these multiple interactions might be better viewed as principally providing efferent information from the posterior medial temporal lobe. Both a subcortical diencephalic route (via the fornix) and a cortical cingulate route (via retrosplenial cortex) can be distinguished. These routes provide indirect pathways for hippocampal interactions with prefrontal cortex, with the preponderance of both sets of connections arising from the more posterior hippocampal regions. These multi-stage connections complement the direct hippocampal projections to prefrontal cortex, which principally arise from the anterior hippocampus, thereby creating longitudinal functional differences along the anterior–posterior plane of the hippocampus.

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