%0 Journal Article %J Nature Communications %D 2017 %T Neuronal population coding of perceived and memorized visual features in the lateral prefrontal cortex %A Diego Mendoza-Halliday %A Julio Martinez-Trujillo %X

The primate lateral prefrontal cortex (LPFC) encodes visual stimulus features while they are perceived and while they are maintained in working memory. However, it remains unclear whether perceived and memorized features are encoded by the same or different neurons and population activity patterns. Here we record LPFC neuronal activity while monkeys perceive the motion direction of a stimulus that remains visually available, or memorize the direction if the stimulus disappears. We find neurons with a wide variety of combinations of coding strength for perceived and memorized directions: some neurons encode both to similar degrees while others preferentially or exclusively encode either one. Reading out the combined activity of all neurons, a machine-learning algorithm reliably decode the motion direction and determine whether it is perceived or memorized. Our results indicate that a functionally diverse population of LPFC neurons provides a substrate for discriminating between perceptual and mnemonic representations of visual features.

%B Nature Communications %V 8 %8 June 2017 %G eng %U https://doi.org/10.1038/ncomms15471 %9 Article No. 15471 %0 Journal Article %J Trends in Neurosciences %D 2017 %T Sustained Activity Encoding Working Memories: Not Fully Distributed %A Leavitt, M.L. %A Diego Mendoza-Halliday %A Martinez-Trujillo J.C. %K working memory sustained activity neurophysiology fMRI primate review %X

Working memory (WM) is the ability to remember and manipulate information for short time intervals. Recent studies have proposed that sustained firing encoding the contents of WM is ubiquitous across cortical neurons. We review here the collective evidence supporting this claim. A variety of studies report that neurons in prefrontal, parietal, and inferotemporal association cortices show robust sustained activity encoding the location and features of memoranda during WM tasks. However, reports of WM-related sustained activity in early sensory areas are rare, and typically lack stimulus specificity. We propose that robust sustained activity that can support WM coding arises as a property of association cortices downstream from the early stages of sensory processing.

%B Trends in Neurosciences %V 40 %P 328-346 %8 June 2017 %G eng %U https://www.sciencedirect.com/science/article/pii/S0166223617300711 %N 6 %R https://doi.org/10.1016/j.tins.2017.04.004 %0 Book Section %B Mechanisms of Sensory Working Memory: Attention and Performance XXV. %D 2015 %T Working Memory Representations of Visual Motion along the Primate Dorsal Visual Pathway %A Diego Mendoza-Halliday %A Torres, S. %A Julio Martinez-Trujillo %X

Mechanisms of Sensory Working Memory: Attention and Performance XXV provides an update on the research surrounding the memory processes that are crucial for many facets of cognitive processing and experience, with new coverage of emerging areas of study, including a new understanding of working memory for features of stimuli devoid of verbal, phonological, or long-term memory content, such as memory for simple visual features (e.g., texture or color), simple auditory features (e.g., pitch), or simple tactile features (e.g., vibration frequency), now called sensory memory to distinguish from verbal memory.

This contemporary focus on sensory memory is just beginning, and this collection of original contributions provides a foundational reference for the study mechanisms of sensory memory.

 

 

%B Mechanisms of Sensory Working Memory: Attention and Performance XXV. %I Elsevier Inc. %G eng %U https://www.sciencedirect.com/book/9780128013717/mechanisms-of-sensory-working-memory %0 Journal Article %J Nature Neuroscience %D 2014 %T Sharp emergence of feature-selective sustained activity along the dorsal visual pathway %A Diego Mendoza-Halliday %A Santiago Torres %A Julio Martinez-Trujillo %X

Sustained activity encoding visual working memory representations has been observed in several cortical areas of primates. Where along the visual pathways this activity emerges remains unknown. Here we show in macaques that sustained spiking activity encoding memorized visual motion directions is absent in direction-selective neurons in early visual area middle temporal (MT). However, it is robustly present immediately downstream, in multimodal association area medial superior temporal (MST), as well as and in the lateral prefrontal cortex (LPFC). This sharp emergence of sustained activity along the dorsal visual pathway suggests a functional boundary between early visual areas, which encode sensory inputs, and downstream association areas, which additionally encode mnemonic representations. Moreover, local field potential oscillations in MT encoded the memorized directions and, in the low frequencies, were phase-coherent with LPFC spikes. This suggests that LPFC sustained activity modulates synaptic activity in MT, a putative top-down mechanism by which memory signals influence stimulus processing in early visual cortex.

%B Nature Neuroscience %V 7 %8 09/2014 %G eng %U http://www.nature.com/neuro/journal/v17/n9/abs/nn.3785.html %N 9 %& 1255 %R doi:10.1038/nn.3785 %0 Journal Article %J Journal of Vision %D 2011 %T Combined effects of feature-based working memory and feature-based attention on the perception of visual motion direction %A Diego Mendoza-Halliday %A Megan Schneiderman %A Christian Kaul %A Julio Martinez-Trujillo %B Journal of Vision %V 11 %G eng %N 1 %& 11 %0 Journal Article %J Journal of Vision %D 2011 %T Combined effects of feature-based working memory and feature-based attention on the perception of visual motion direction %A Diego Mendoza-Halliday %A Schneiderman, M. %A Kaul, C. %A Julio Martinez-Trujillo %K feature-based attention %K motion direction %K motion perception %K Psychophysics %K working memory %X

We investigated whether human subjects’ability to identify the direction of a brief pulse of coherent motion in a random-dotpattern (RDP) was influenced by: (a) maintaining in working memory the direction of motion of an RDP previously presentedfar from the pulse (feature-based working memory or FBWM,Experiment 1), (b) attending to the direction of an RDPco-occurring with but far from the pulse (feature-based attention or FBA,Experiment 2), and (c) both FBWM and FBA actingsimultaneously (Experiment 3). In thefirst two experiments, pulse direction identification performance was higher when theremembered direction (FBWM) or the direction of the concurrently attended RDP (FBA) matched the pulse direction thanwhen it was opposite. InExperiment 3, performance was highest when both the remembered and the attended directionsmatched the pulse direction (combined effects of FBWM and FBA), it was intermediate when only one of them matched thepulse direction, and it was lowest when neither matched the pulse direction. Our results demonstrate that both feature-based working memory and feature-based attention can individually modulate the perception of motion direction and thatwhen acting together they produce an even larger modulation.

%B Journal of Vision %V 11 %G eng %U http://www.journalofvision.org/content/11/1/11 %N 1 %R doi:10.1167/11.1.11