NEUROBIOLOGY OF SLEEP, MEMORY AND COGNITION

Our goal


Humans and non-human animals are constantly exposed to large amounts of information of varying importance. Some of this information is stored in the brain as distinct memories. The memories are further processed, organized and gradually integrated into consistent and coherent representations of events, mental concepts, and ultimately into understanding of the world. These integrated complex mental structures are sometimes called cognitive maps, or cognitive schemata. We are interested in the processes of organizing different, mutually related streams of information, representations, and memories in the mind. We study these processes during wakefulness and sleep, under normal conditions as well as in brain disorders in humans and in animal models.



Our approach


In animal experiments - our primary approach - we record populations of hippocampal and neocortical neurons in rats as they explore environments, perform different cognitive tasks and learn. We study how neuronal activity represents different aspects of experience - for example, spatial and temporal context, identity of objects or conspecifics. We then study how the activity of different neurons is organized to create an integrated representation of an experience. We think of the network-level organization of activity in the context of theoretical concepts of cell assemblies and attractor networks, and develop and test these hypotheses with the help of our experimental data.

Sleep plays an important role in the consolidation and organization of learned knowledge. Therefore, we study neuronal processes occurring during sleep that underlie the cognitive processes of memory consolidation. According to our hypothesis, some of the cognitive impairments that accompany brain disorders are associated with impaired or disorganized activity in neuronal networks of the brain. To understand such neuronal and cognitive disorganization, we also record and study neuronal activity in animal models of brain pathologies, such as posttraumatic stress disorder, psychosis, or obsessive-compulsive disorder.

Our research into the organization of spatial representations in humans is spearheaded by Dr. Kamil Vlcek. We design and use tasks in controlled physical environments and in virtual reality to study different aspects of spatial information processing in healthy people as well as in brain disorders such as Alzheimer's disease, schizophrenia or epilepsy.







Examples of action potentials recorded from five neurons (shown in different colors) from an active freely moving rat.
The action potentials of all five neurons are recorded from the same four electrodes placed very close to each other (so-called tetrode). The different action potential shapes of the same cell are result of the slightly different position of an individual cell relative to each of the four electrodes.






Raster plots showing time series of action potentials of 15 simultaneously recorded hippocampal neurons while a rat was exploring two different environments (experimental rooms). One 15-minute session in room B was flanked by two sessions in room A. Notice that the intensity (frequency) of action potential discharge of recorded neurons differs between the two rooms.






Spatial organization of discharge of four neurons from the hippocampus and anterior cingulate cortex while a rat was walking in a square box with three objects. The rat's trajectory is shown in black, positions of actions potentials are shown as colored dots..






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▲ Examples of electroencephalogram (EEG) and electromyogram (EMG) recordings of rodent brain and muscle activity in different stages of wakefulness and sleep. ► Frequency composition of EEG signal during 30 minute recording of mouse activity. Red color indicates strong presence, green and blue colors indicate weak presence of particular frequencies in the signal. Corresponding hypnogram with different stages of sleep and wakefulness is shown below.







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A rat operating a feeder in one of our experiments. ◄ The rat is selecting one of the four feeders (each marked by a different object) on a rotating carousel. ▲ The rat pulls and opens the feeder with white cylinder and releases a food pellet.