Graded remapping of hippocampal ensembles under sensory conflicts

Low rate hippocampal delay period activity encodes behavioral experience

Remembering what just happened is a crucial prerequisite to form long-term memories but also for establishing and maintaining working memory. So far there is no general agreement about cortical mechanisms that support short-term memory. Using a classifier-based decoding approach, we report that hippocampal activity during few sparsely distributed brief time intervals contains information about the previous sensory motor experience of rodents. These intervals are characterized by only a small increase of firing rate of only a few neurons. These low-rate predictive patterns are present in both working memory and non-working memory tasks, in two rodent species, rats and Mongolian gerbils, are strongly reduced for rats with medial entorhinal cortex lesions, and depend on the familiarity of the sensory-motor context.

Neural ensembles in navigation: From single cells to population codes

The brain can represent behaviorally relevant information through the firing of individual neurons as well as the coordinated firing of ensembles of neurons. Neurons in the hippocampus and associated cortical regions participate in a variety of types of ensembles to support navigation. These ensemble types include single cell codes, population codes, time-compressed sequences, behavioral sequences, and engrams. We present the physiological basis and behavioral relevance of ensemble firing. We discuss how these traditional definitions of ensembles can constrain or expand potential analyses due to the underlying assumptions and abstractions made. We highlight how coding can change at the ensemble level while underlying single cell codes remain intact. Finally, we present how ensemble definitions could be broadened to better understand the full complexity of the brain.

Low Rate Hippocampal Delay Period Activity Encodes Behavioral Experience

Remembering what just happened is a crucial prerequisite to form long-term memories but also for establishing and maintaining working memory. So far there is no general agreement about cortical mechanisms that support short-term memory. Using a classifier-based decoding approach, we report that hippocampal activity during few sparsely distributed brief time intervals contains information about the previous sensory motor experience of rodents. These intervals are characterized by only a small increase of firing rate of only a few neurons. These low-rate predictive patterns are present in both working memory and non-working memory tasks, in two rodent species, rats and Mongolian gerbils, are strongly reduced for rats with medial entorhinal cortex lesions, and depend on the familiarity of the sensory-motor context.

Decreased cognitive function of ALG13KO female mice may be related to the decreased plasticity of hippocampal neurons

Asparagine-linked glycosylation 13 (ALG13) is an X-linked gene that encodes a protein involved in the glycosylation of the N-terminus. ALG13 deficiency leads to ALG13-congenital disorders of glycosylation (ALG13-CDG), usually in females presenting with mental retardation and epilepsy. Cognitive function is an important function of the hippocampus, and forms the basis for learning, memory and social abilities. However, researchers have not yet investigated the effect of ALG13 on hippocampal cognitive function. In this study, the exploration, learning, memory and social abilities of ALG13 knockout (KO) female mice were decreased in behavioral experiments. Golgi staining demonstrated a decrease in the complexity of hippocampal neurons. Western blot and immunofluorescence staining of the synaptic plasticity factors postsynaptic density protein 95 (PSD95) and synaptophysin (SYP) displayed varying degrees of decline. In other words, the KO of ALG13 may have reduced the expression of PSD95 and SYP in the hippocampus of female mice. Moreover, it may have lowered the synaptic plasticity in various areas of the hippocampus, thus resulting in decreased dendrite length, complexity, and dendrite spine density, which affected the hippocampal function and reduced the cognitive function in female mice.

Neural kernels for recursive support vector regression as a model for episodic memory

Retrieval of episodic memories requires intrinsic reactivation of neuronal activity patterns. The content of the memories is thereby assumed to be stored in synaptic connections. This paper proposes a theory in which these are the synaptic connections that specifically convey the temporal order information contained in the sequences of a neuronal reservoir to the sensory-motor cortical areas that give rise to the subjective impression of retrieval of sensory motor events. The theory is based on a novel recursive version of support vector regression that allows for efficient continuous learning that is only limited by the representational capacity of the reservoir. The paper argues that hippocampal theta sequences are a potential neural substrate underlying this reservoir. The theory is consistent with confabulations and post hoc alterations of existing memories.