Kreiman Lab News

CBMM: The brain’s operating system. Research Update 2

We hope that you will be able to join next week’s research meeting with presentations by Mengmi Zhang and Jie Zheng, Kreiman Lab.

CBMM Research Meeting

Title: Module 2 Research presentation

Date/Time: October 26, 2021, 4:00 pm to 5:30 pm ET

Jie Zheng
Jie Zheng

Jie Zheng‘s presentation (in person):

Title: Neurons that structure memories of ordered experience in human

 Abstract: The process of constructing temporal associations among related events is essential to episodic memory. However, what neural mechanism helps accomplish this function remains unclear. To address this question, we recorded single unit activity in humans while subjects performed a temporal order memory task. During encoding, subjects watched a series of clips (i.e., each clip consisted of 4 events) and were later instructed to retrieve the ordinal information of event sequences. We found that hippocampal neurons in humans could index specific orders of events with increased neuronal firings (i.e., rate order cells) or clustered spike timing relative to theta phases (i.e., phase order cells), which are transferrable across different encoding experiences (e.g., different clips). Rate order cells also increased their firing rates when subjects correctly retrieved the temporal information of their preferred ordered events. Phase order cells demonstrated stronger phase precessions at event transitions during encoding for clips whose ordinal information was subsequently correct retrieved. These results not only highlight the critical role of the hippocampus in structuring memories of continuous event sequences but also suggest a potential neural code representing temporal associations among events.

Mengmi Zhang
Mengmi Zhang

Mengmi Zhang‘s [virtual] presentation:

Title: Visual Search Asymmetry: Deep Nets and Humans Share Similar Inherent Biases

Abstract: Visual search is a ubiquitous and often challenging daily task, exemplified by looking for the car keys at home or a friend in a crowd. An intriguing property of some classical search tasks is an asymmetry such that finding a target A among distractors B can be easier than finding B among A. To elucidate the mechanisms responsible for asymmetry in visual search, we propose a computational model that takes a target and a search image as inputs and produces a sequence of eye movements until the target is found. The model integrates eccentricity-dependent visual recognition with target-dependent top-down cues. We compared the model against human behavior in six paradigmatic search tasks that show asymmetry in humans. Without prior exposure to the stimuli or task-specific training, the model provides a plausible mechanism for search asymmetry. We hypothesized that the polarity of search asymmetry arises from experience with the natural environment. We tested this hypothesis by training the model on an augmented version of ImageNet where the biases of natural images were either removed or reversed. The polarity of search asymmetry disappeared or was altered depending on the training protocol. This study highlights how classical perceptual properties can emerge in neural network models, without the need for task-specific training, but rather as a consequence of the statistical properties of the developmental diet fed to the model. Our work will be presented in the upcoming Neurips conference, 2021.

See also: Gupta SK, Zhang M, Wu CC, Wolfe JM, Kreiman G (2021). Visual search asymmetry: deep nets and humans share similar inherent biases. NeurIPS PDF

Kreiman Lab News

Jerry Wang publishes landmark study on human brain interactome

Wang et al 2021 Human Brain Interactome
Wang et al Cell Reports 2021. Human brain interactome

Cognition relies on rapid and robust communication between brain areas. Wang et al. leverage multi-day intracranial field potential recordings to characterize the human mesoscopic functional interactome. The methods are validated using monkey anatomical and physiological data. The human interactome reveals small-world properties and is modulated by sleep versus awake state.

  • Recorded continuous intracranial field potentials for 5 days in 48 human subjects
  • Characterized functional mesoscopic interactome assessed by pairwise coherence
  • Validated methods using anatomical and physiological interactions in monkeys
  • Human functional interactome shows small-world graph and changes with brain state

Mesoscopic functional interactions in the human brain reveal small-world properties

Wang J, Anderson WS, Masen JR, Kreiman G

Cell Reports 8 (6), 2021



Supplementary Material

Kreiman Lab News

Congratulations to Leonardo Pollina!

Leonardo Pollina
Leonardo Pollina, M. Sc.

Leonardo Pollina successfully defended his Master’s Thesis

His thesis is entitled: “Combining neurophysiology and computational modeling through VGG19”

Leonardo’s work was supported by the Bertarelli Foundation

Kreiman Lab News

Congratulations Dr. Jerry Wang!

Jerry Wang Acadia
Jerry Wang climbing Bee Hive Trail in Acadia, circa 2017

February 16, 2021. Dr. Jerry Wang has successfully defended his Ph.D. thesis. In the words of the thesis examiners, “Herculean computational work”, “A landmark study”. Congratulations Dr. Wang!

See also Jerry Wang’s recent publication: Wang J, Tao A, Anderson WS, Madsen JR, Kreiman G (2021). Mesoscopic physiological interactions in the human brain reveal small world properties. Cell Reports 36 (8) 109585

Kreiman Lab News

Neurons detect cognitive boundaries to structure episodic memories in humans

Jie Zheng. February 03, 2021

While experience is continuous, memories are organized as discrete events. Cognitive boundaries are thought to segment experience and structure memory, but how this process is implemented remains unclear. We recorded the activity of single neurons in the human medial temporal lobe during the formation and retrieval of memories with complex narratives. Neurons responded to abstract cognitive boundaries between different episodes. Boundary-induced neural state changes during encoding predicted subsequent recognition accuracy but impaired event order memory, mirroring a fundamental behavioral tradeoff between content and time memory. Furthermore, the neural state following boundaries was reinstated during both successful retrieval and false memories. These findings reveal a neuronal substrate for detecting cognitive boundaries that transform experience into mnemonic episodes and structure mental time travel during retrieval.