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HSE scientists used magnetoencephalography and magnetic resonance imaging to study how people store and process temporal and spatial information in their working memory. The experiment has demonstrated that dealing with temporal information is more challenging for the brain than handling spatial information. The brain expends more resources when processing temporal data and needs to employ additional coding using 'spatial' cues. The paper has been published in the Journal of Cognitive Neuroscience.
The study was carried out within the framework of the HSE Basic Research Programme.
Working memory is a temporary mental storage system with limited capacity, used for immediate processing of information. It plays a key role in the memorisation and utilisation of data, including temporal and spatial information, as well as logical reasoning and decision-making. Numerous mental problems such as dysgraphia, dyslexia, depression, and obsessive-compulsive disorder, are linked to working memory anomalies and disorders.
A team of scientists at HSE University conducted an experiment to investigate the neuronal mechanisms underlying the processing and storage of temporal and spatial information in working memory. The experiment involved 26 participants, with an equal distribution of men and women.
During the experiment, the subjects were asked to memorise spatial and temporal stimuli. First, the participants were shown cue words indicating what they were required to remember: either 'where'—indicating the location in which the stimuli were presented, or 'when'—referring to the sequence of their appearance. Then, each participant was presented with four shapes appearing sequentially in one of the four corners. If the initial cue was 'where,' the subjects had to memorise in which corner the shape appeared; if the cue was 'when,' they needed to list the order in which the shapes were shown. Throughout the experiment, the researchers recorded the subjects' brain activity using magnetoencephalography (MEG).
The experiment demonstrated that participants performed equally well whether memorising sequences or locations. However, an analysis of brain activity data using the MEG method revealed differences in how information about time and space is stored. For participants to recall the sequence as accurately as the location, extra effort was necessary, evident in the additional activation of specific brain areas—namely, the posterior parietal lobe in the beta frequency range and the anterior precentral region in the theta frequency range.
The number and intensity of fluctuations in neuronal activity in the beta frequency range were notably more pronounced in the parietal lobe, suggesting a conversion of temporal information into spatial representation. We suppose that the concept of time is sufficiently complex for the human brain to require additional spatial 'cues' to effectively process temporal information in working memory.
Electrical activity defines the neuronal architecture—it can manifest in a single zone of the brain, or it can occur across multiple zones when they are engaged in the same function. The scientists have discovered that for each frequency, the storage of information regarding sequence and space involves entirely distinct neural architecture, or connectivity between brain regions.
For example, in the theta range, when the sequence was being stored, the scientists observed connectivity primarily between the posterior regions of the right hemisphere, either interconnecting or linking with the central regions of the brain in the left hemisphere. When storing information about space in the theta range, the brain established neuronal connections in the anterior regions, with the majority of these connections being interhemispheric.
An examination of such interconnected activity in different brain regions reveals distinct organisation, number, and intensity of connections between its parts when memorising sequences and locations of shapes. The researchers conclude that storing temporal sequences and spatial locations in working memory involve fundamentally different processes.
The findings of the study could aid in cognitive rehabilitation and treatment of disorders associated with impairments in working memory. With precise knowledge of the brain area responsible for a specific function of working memory, clinicians and scientists can focus on targeted stimulation of specific brain areas to alleviate the symptoms of disorders.
IQ
Nikita Otstavnov
Junior Research Fellow, International Laboratory of Social Neurobiology, Institute for Cognitive Neuroscience, HSE University