A non-navigational test of incidental spatial learning was used to determine whether hippocampal damage causes temporally-graded retrograde amnesia (TGRA) for allocentric-spatial information. Rats were exposed to two identical objects in a circular open field for 7 min on seven consecutive days. In the 1-3 days after the last day of familiarization, rats received neurotoxic lesions of the hippo...

The hippocampal formation (HF) of food-storing birds is larger than non-storing species, and the size of the HF in food-storing Black-Capped Chickadees (Poecile atricapillus) varies seasonally. We examined whether the volume of the septum, a medial forebrain structure that shares reciprocal connections with the HF, demonstrates the same species and seasonal variation as has been shown in the HF...

We have studied 5-hydroxytryptamine (5-HT) release in the hippocampal formation following electrical stimulation of the dorsal and median raphé nuclei in the behaving rat. The primary finding in this study is a decrease in neuronal release of serotonin in the dorsal hippocampal formation following electrical stimulation of either the dorsal or median raphé nucleus in conscious rats. At no time ...

WHEN DISCUSSING A BRAIN FUNCTION SUCH AS MEMORY, one should relate it to brain plasticity. One definition of plasticity is an alternative way of performing the same function. Anecdotal evidence suggests that the human brain can perform amazing memory feats in unexpected, alternative ways. For example, the established ability of savants (individuals with partial brain damage) to memorize events,...

There is a growing interest in how temporal order of episodic memories is represented within the medial temporal lobe (MTL). Animal studies suggest that the hippocampal formation (HF) is critical for retrieving the temporal order of past experiences. However, human imaging studies that have tested recency discrimination between pairs of previously encoded items have generally failed to report H...

Recently, it was found that microglia regulated synaptic remodeling of the developing brain, but their mechanisms have not been well understood. In this study, the action of microglia on neuronal synapse formation was investigated, and the primary target of microglial processes was discovered. When the developing microglia were applied to cultured hippocampal neurons without direct contact, the...

Older people with declining cognitive function typically display deficits in declarative memory processes, often most evident on tests of associative learning (AL). The hippocampal formation (HF) is thought to be critically involved in the encoding and retrieval of such associations, consistent with neuroimaging findings that the HF is damaged in early stages of neurodegenerative disease and in...

Neuropsychological data in primates demonstrated a pivotal role of the hippocampal formation (HF) and parahippocampal gyrus (PH) in navigation and episodic memory. To investigate the role of HF and PH neurons in environmental scaling in primates, we recorded neuronal activities in the monkey HF and PH during virtual navigation (VN) and pointer translocation (PT) tasks. The monkeys had to naviga...

The relationships between the entorhinal cortex (EC) and the hippocampal formation (Hipp) field potentials were examined in the present study. The detailed analyses of the signal let us group the patterns of theta appearance into three categories: (1) Theta rhythm dominating in both recordings from the EC and from the Hipp (2) Theta rhythm dominating in the Hipp with irregular activity in the E...