Imagine seeing several objects on a table and, after a short delay, having to reach for one of them even though they are no longer visible. This seemingly simple task requires complex cooperation between several parts of the brain. A new study arising from a collaboration between researchers from the Laboratory of Neurophysiology of Memory at IPHYS and Second Faculty of Medicine, Charles University – Motol University Hospital (EpiRec center) reveals how these areas communicate when we remember what we saw and where, and then act on that information.
The traditional view of visual perception distinguished two main information-processing streams in the brain: an upper stream in the parietal lobe, which controls immediate movements and discriminates spatial positions, and a lower stream in the temporal lobe, which recognizes objects and enables actions guided by stored memories. However, new research shows that reality is more complex: the two areas cooperate much more closely than previously thought.
“We took advantage of a unique opportunity to study patients with epilepsy who had temporarily implanted electrodes directly in the brain. While the patients performed a spatial memory task – remembering the positions of objects and, after several seconds, pointing to one of them – the electrodes recorded activity directly from different brain areas,” explains the study’s lead author, Kamil Vlček.
The results showed that the two visual streams do not operate independently. During the waiting period, brain activity increased simultaneously in both streams, specifically in the so‑called alpha waves. Their rhythms synchronized, as if these brain regions were passing information to each other, suggesting that both areas jointly maintain spatial information in memory. Even more interesting was the finding that when patients had to remember not only the position but also the identity of the object, the hippocampus – one of the key memory centres in the brain – also became involved, showing stronger activity and more intensive communication with the parietal region.
“Our findings thus support the idea that memory‑guided motor behaviour is not the work of a single specialized area, but of interacting networks in different parts of the brain,” adds Kamil Vlček. For clinical practice, it is essential to have a better understanding of the areas and their interconnections that contribute to spatial orientation and memory. In the future, this may help with planning neurosurgical procedures to minimize the risk of memory and orientation disorders, as well as with targeted rehabilitation of patients with damage to these functions.
Reference: Moraresku S., Hammer J., Dimakopoulos V., Kajsova M., Janca R., Jezdik P., Kalina P., Marusic P., Vlcek K.: Neural Dynamics of Visual Stream Interactions During Memory-Guided Actions Investigated by Intracranial EEG. Neurosci. Bull. 41(8):1347–1363 (2025). IF = 5.8, DOI: 10.1007/s12264-025-01371-x
Picture legend:
IPL (inferior parietal lobule) is part of the dorsal visual stream that, as a component of working memory, helps maintain spatial information about the position of an object while it is hidden.
VTC (ventral temporal cortex) is part of the ventral visual stream that identifies objects and retains information about their identity.
HIP (hippocampus) is a structure essential for declarative memory, which links different types of information, such as those about an object’s identity and position.
The test consisted of several phases:
Fixation – shortly before object presentation, the subject fixated on a central cross. In the graphs, this phase is labeled as Baseline.
Encoding – memorization of the position and, if applicable, the identity of the object closer to the cross. The objects were either identical (same) or different (different); in the latter case, the task was to remember which of the two objects was closer to the cross.
Delay – a pause during which the objects were hidden.
Recall – retrieval phase, where the task was to indicate the position of the object that had been closer to the cross.
In the bottom-right graph, these four phases are marked simply as f, e, d, and r.
PLV (phase locking value), slow theta – a measure of synchronization of the theta rhythm between two regions.
