Both fornix and anterior thalamic, but not mammillary, lesions disrupt delayed non-matching-to-position memory in rats

Aggleton, John Patrick; Keith, A.B.; Sahgal, Arjun

doi:10.1016/s0166-4328(05)80020-8

Cited by 117 publications

(74 citation statements)

References 31 publications

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“…The spared thalamic connections are particularly relevant as direct comparisons have shown that anterior thalamic lesions are more disruptive than mammillary body lesions on some (Sutherland and Rodriguez, 1989;Aggleton et al, 1991;Aggleton et al, 1995), but not all (Aggleton et al, 1995;Gaffan et al, 2001), tests of spatial memory. In addition, anterior thalamic and fornix lesions can have comparable disruptive effects on spatial tasks (e.g., Sutherland and Rodriguez, 1989;Aggleton et al, 1991;Gaffan et al, 2001) and disconnection evidence shows that the anterior thalamic nuclei function conjointly with the hippocampus on the same spatial tasks used in this study Henry et al, 2004). Thus, one explanation for the greater impact of complete fornix lesions than descending postcommissural fornix lesions is that after the latter surgery spatial memory is still supported by the dense hippocampal formation (anterior thalamic projections.…”

Section: Discussionmentioning

confidence: 99%

Selective disconnection of the hippocampal formation projections to the mammillary bodies produces only mild deficits on spatial memory tasks: Implications for fornix function

et al. 2011

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ABSTRACT:It is now clear that the integrity of the fornix is important for normal mnemonic function. The fornix, however, is a major white matter tract, carrying numerous hippocampal formation afferents and efferents, and it is not known which specific components support memory processes. Established theories of extended hippocampal function emphasize the sequential pathway from the hippocampal formation (i.e., subicular complex) to the mammillary bodies and, thence, to the anterior thalamus, as pathology in each of these structures is implicated in anterograde amnesia in humans and spatial memory deficits in rats. The specific importance of the hippocampal formation projections that just innervate the mammillary bodies has, however, never been tested. This study isolated these specific projections in the rat by selectively cutting the descending component of the postcommissural fornix. Two successive, cohorts of rats with these tract lesions were tested on working memory tasks in the water-maze, T-maze, and radial-arm maze. Disconnecting the descending postcommissural fornix had only a mild effect or sometimes no apparent effect on the performance of these spatial memory tasks, even though tracing experiments confirmed the loss of hippocampal formation-mammillary projections. One implication is that the spatial deficits found in rats following standard fornix lesions are only partly attributable to the loss of projections from the hippocampal formation to the mammillary bodies. Perhaps more surprising, the behavioral impact of cutting the descending postcommissural fornix in rats appeared appreciably less than the effect of either mammillary body or mammillothalamic tract lesions. The present experiments show that the mammillary bodies can still effectively support spatial memory in the absence of their dense subicular complex inputs, so revealing the importance of the other afferents for sustaining mammillary body function. This new evidence for independent functions shows that the mammillary bodies are more than just a hippocampal relay. V V C 2010 Wiley-Liss, Inc.

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Section: Discussionmentioning

confidence: 99%

Selective disconnection of the hippocampal formation projections to the mammillary bodies produces only mild deficits on spatial memory tasks: Implications for fornix function

et al. 2011

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“…Furthermore, restricted pathologies from tumors and traumatic injury also reveal the contributions of the mammillary bodies to episodic memory (Dusoir et al, 1990;Tsivilis et al, 2008). Importantly, animal models using localized lesions reveal that mammillary bodies or MTT lesion impairments has less severe effects on spatial memory tasks than those following ATN lesions, the latter being often comparable to fornix lesions (Aggleton et al, 1991(Aggleton et al, , 1995, but also see Vann and Albasser, 2009). The above-mentioned clinical findings and lesion studies strongly suggest that the anterior thalamus functionally complements the hippocampal region for memory processing .…”

Section: Discussionmentioning

confidence: 99%

Hippocampal inputs mediate theta-related plasticity in anterior thalamus

et al. 2011

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Hippocampally-driven oscillatory activity at theta frequency is found in the diencephalon, but an understanding of the fundamental role of theta in the hippocampo-diencephalic circuit remains elusive. An important strategy in determining how activity modifies oscillatory properties of hippocampo-diencephalic circuitry comprises investigations of anterior thalamic responses to their main inputs: the descending dorsal fornix and the ascending mammillothalamic tract. Here, we show that the amplitude of thalamic theta spectral power selectively increases after plasticityinducing stimulation of the dorsal fornix, but not of the mammillothalamic tract in urethaneanaesthetized young male rats. Furthermore, we show that low-frequency stimulation (LFS) significantly augments the fornix-driven theta ratio (theta over delta power, T-ratio), in parallel with depressing thalamic synaptic responses. However, the mammillothalamic synaptic response after LFS did not correlate with the slow band of theta oscillation (low T-ratio), but did correlate positively with the fast band of theta oscillation (high T-ratio). Our data demonstrate that the descending direct fornix projection is a pathway that modulates theta rhythm in the hippocampodiencephalic circuit, resulting in dynamic augmentation of thalamic neuronal responsiveness. These findings suggest that hippocampal theta differentially affects synaptic integration in the different structures with which the hippocampus is reciprocally connected. Keywordsanterior thalamic nuclei; fornix; mammillothalamic tract; synaptic plasticity; theta oscillation; LTP The functioning of the thalamus and the hippocampus cannot be fully elucidated without considering them as a unified network (Steriade, 2001;Warburton et al., 2001). In this context, hippocampal oscillations would be expected to have an impact on the neuronal activity of the anterior thalamic nuclei (ATN) but how the signals are actually processed through the hippocampo-diencephalic loop remains poorly understood. Large neuronal populations in ATN oscillate with frequency of 6-11 Hz, in the range of theta rhythm (Vertes et al., 2001;Tsanov et al., 2011a). Theta oscillations are a characteristic feature also of the main regions providing anterior thalamic inputs: the hippocampal formation and the medial mammillary bodies, that is the "medial" hippocampo-diencephalic system Theta rhythm has been especially related to the processes of episodic memory formation in the extended hippocampal system (Buzsáki, 2005). The hippocampus receives two main types of input: the first one is the theta input from the medial septum, which reverberates through hippocampo-diencephalic loop (Fig. 1A). The second hippocampal input is a highly-processed sensory information originating from multiple neocortical regions. The temporal convergence of activity from neocortical and diencephalic inputs would result in long-term storage of the encoded information. Because theta activity induces a fluctuation in cellular excitability, the probability tha...

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“…Learning in this task is usually inferred from the day-to-day improvements in task performance with rats typically making an increasing number of correct choices over the course of 1 or 2 weeks. Several interesting versions of this task have been subsequently developed, including most notably the 'delayed non-matching to sample' (DNMS) and 'delayed matching to sample' (DMS) versions, in which an interval is imposed between the first four choices and the last four [3,203] ( Table 1). In both tasks, each trial has a 'sample phase' where the rats are allowed to collect food rewards from four arms (previously defined by the researcher), whilst the other four arms are blocked, and following a set interval (5 min-24 h), a 'choice phase' during which the rat is returned to the maze and required to locate the remaining four food rewards (with all eight arms available).…”

Section: Spatial Tasks With Rodentsmentioning

confidence: 99%

The impact of flavonoids on spatial memory in rodents: from behaviour to underlying hippocampal mechanisms

et al. 2009

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Emerging evidence suggests that a group of dietary-derived phytochemicals known as flavonoids are able to induce improvements in memory, learning and cognition. Flavonoids have been shown to modulate critical neuronal signalling pathways involved in processes of memory, and therefore are likely to affect synaptic plasticity and long-term potentiation mechanisms, widely considered to provide a basis for memory. Animal dietary supplementation studies have further shown that flavonoidrich foods are able to reverse age-related spatial memory and spatial learning impairments. A more accurate understanding of how a particular spatial memory task works and of which aspects of memory and learning can be assessed in each case, are necessary for a correct interpretation of data relating to diet-cognition experiments. Further understanding of how specific behavioural tasks relate to the functioning of hippocampal circuitry during learning processes might be also elucidative of the specific observed memory improvements. The overall goal of this review is to give an overview of how the hippocampal circuitry operates as a memory system during behavioural tasks, which we believe will provide a new insight into the underlying mechanisms of the action of flavonoids on cognition.

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Both fornix and anterior thalamic, but not mammillary, lesions disrupt delayed non-matching-to-position memory in rats

Cited by 117 publications

References 31 publications

Selective disconnection of the hippocampal formation projections to the mammillary bodies produces only mild deficits on spatial memory tasks: Implications for fornix function

Selective disconnection of the hippocampal formation projections to the mammillary bodies produces only mild deficits on spatial memory tasks: Implications for fornix function

Hippocampal inputs mediate theta-related plasticity in anterior thalamus

The impact of flavonoids on spatial memory in rodents: from behaviour to underlying hippocampal mechanisms

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