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Pieter R Roelfsema

Publications and source records attributed to Pieter R Roelfsema.

6 recordsLinked to original sources
PubMed2026

A systematic review of macaque brain stimulation: Trends and future directions.

Neurostimulation techniques can powerfully modulate neural circuit activity and provide causal insights into the relationship between brain function and behavior. Macaque monkeys have long been a key animal model for brain stimulation studies. While stimulating the macaque brain with one or a few electrodes has already taught us much about brain function and dysfunction, recent technological advances promise a future with more precise stimulation using many more electrodes. However, such possibilities also increase the number of choices an experimenter has when designing their study. We can learn from a rich past, but a comprehensive overview of which brain regions have been studied and with what stimulation parameters is lacking. Here, we present a PRISMA-compliant systematic review of 734 macaque brain stimulation studies using electrical and/or optogenetic stimulation. We find a striking bias in which brain areas have traditionally been stimulated: a mere 10 brain regions account for half of all studies, with the remainder of studies investigating approximately 150 other areas. Across studies, stimulation frequency robustly predicted direct behavioral effects independent of brain region, while amplitude did not. Future studies could more systematically explore less studied regions through lower stimulation frequencies (e.g., 20-50 Hz) alongside established ranges (∼200 Hz). Tools such as fMRI or optical imaging can capture neural circuit engagement evoked by these frequencies, even when behavioral effects are absent or remain subtle. Our synthesis offers a guide towards the next steps in high-channel-count, high-precision stimulation approaches.

Animals↗
PubMed2003

Subtask sequencing in the primary visual cortex.

Complex visual tasks can usually be decomposed into a number of simpler subtasks. Whether such subtasks are solved serially or in parallel is subject to considerable debate. Here we investigate how subtasks are coordinated in time by recording from the primary visual cortex of macaque monkeys. The animals were trained to perform both a simple and a composite task. In the simple task, they had to mentally trace a target curve while ignoring a distractor curve. Neuronal responses in the primary visual cortex to the target curve were enhanced relative to responses to the distractor curve 130 ms after stimulus appearance. In the composite task, the monkeys searched for a colored marker and traced a curve that was attached to this marker. In an initial phase of the trials, neuronal responses reflected visual search, and the response enhancement due to curve tracing now occurred after 230 ms, 100 ms later than in the simple task. We conclude that subtasks of the composite task are carried out in a structured and sequential manner that can be monitored in the primary visual cortex.

Animals↗
PubMed2002

Figure-ground segregation in a recurrent network architecture.

Here we propose a model of how the visual brain segregates textured scenes into figures and background. During texture segregation, locations where the properties of texture elements change abruptly are assigned to boundaries, whereas image regions that are relatively homogeneous are grouped together. Boundary detection and grouping of image regions require different connection schemes, which are accommodated in a single network architecture by implementing them in different layers. As a result, all units carry signals related to boundary detection as well as grouping of image regions, in accordance with cortical physiology. Boundaries yield an early enhancement of network responses, but at a later point, an entire figural region is grouped together, because units that respond to it are labeled with enhanced activity. The model predicts which image regions are preferentially perceived as figure or as background and reproduces the spatio-temporal profile of neuronal activity in the visual cortex during texture segregation in intact animals, as well as in animals with cortical lesions.

Feedback↗
PubMed2002

Oscillatory neuronal synchronization in primary visual cortex as a correlate of stimulus selection.

Spike and local field potential activity were recorded simultaneously from multiple sites in primary visual cortex of strabismic cats, while monocular stimulation alternated with dichoptic stimulation, inducing interocular rivalry. During interocular rivalry, there is competition between the two nonfusible stimuli presented to the two eyes, and only one stimulus is selected at any time. We biased this competition in three different ways: (1) we exploited the condition that in strabismic cats there is often one dominant eye that is selected for most of the time. (2) We presented the two stimuli with a temporal offset, which biases competition in favor of the newly appearing stimulus. (3) We presented the two stimuli with highly different contrasts, which biases competition in favor of the stimulus with higher contrast. Whenever competition was biased in favor of the stimulus activating the recorded neurons, gamma-frequency synchronization of the respective responses was enhanced, and vice versa. Firing rates showed some differences between stimulation conditions. However, when present, these changes were inversely related to a competitive advantage of the respective stimulus. We hypothesize that enhanced gamma-frequency synchronization in primary visual cortex is a correlate of stimulus selection. Synchronization is likely to be translated into firing rate changes at later processing stages.

Action Potentials↗
PubMed2002

Ocular dominance in extrastriate cortex of strabismic amblyopic cats.

Ocular dominance in extrastriate visual cortex of cats with behaviorally defined strabismic amblyopia was studied using extracellular recording techniques. In area 18, the amblyopic eye drove about as many cells as the normal one. In area posteromedial lateral suprasylvian area (PMLS), about 60% of the cells responded exclusively to stimulation of the normal eye and 30% to stimulation of the amblyopic eye. In area 21a more than 75% of the cells were monocularly driven by the non-amblyopic eye while only 5% were monocularly driven by the amblyopic eye. These findings suggest that ventral pathways (area 21a) are more affected in amblyopia than dorsal pathways (area PMLS).

Amblyopia↗