Biology subjects

Bright, I. M.

Publications and source records attributed to Bright, I. M..

4 recordsLinked to original sources

bioRxiv2024

Ramping cells in rodent mPFC encode time to past and future events via real Laplace transform

In interval reproduction tasks, animals must remember the event starting the interval and anticipate the time of the planned response to terminate the interval. The interval reproduction task thus allows for studying both memory for the past and anticipation of the future. We analyzed previously published recordings from rodent mPFC (Henke et al., 2021) during an interval reproduction task and identified two cell groups by modeling their temporal receptive fields using hierarchical Bayesian models. The firing in the "past cells" group peaked at the start of the interval and relaxed exponentially back to baseline. The firing in the "future cells" group increased exponentially and peaked right before the planned action at the end of the interval. Contrary to the previous assumption that timing information in the brain has one or two time scales for a given interval, we found strong evidence for a continuous distribution of the exponential rate constants for both past and future cell populations. The real Laplace transformation of time predicts exponential firing with a continuous distribution of rate constants across the population. Therefore, the firing pattern of the past cells can be identified with the Laplace transform of time since the past event while the firing pattern of the future cells can be identified with the Laplace transform of time until the planned future event.

neuroscience↗

bioRxiv2024

Ramping dynamics in the frontal cortex unfold over multiple timescales during motor planning

Plans are formulated and refined over the period leading to their execution, ensuring that the appropriate behavior is enacted at just the right time. While existing evidence suggests that memory circuits convey the passage of time through diverse neuronal responses, it remains unclear whether the neural circuits involved in planning behavior exhibit analogous temporal dynamics. Using publicly available data, we analyzed how activity in the frontal motor cortex evolves during motor planning. Individual neurons exhibited diverse ramping activity throughout a delay interval that preceded a planned movement. The collective activity of these neurons was useful for making temporal predictions that became increasingly precise as the movement time approached. This temporal diversity gave rise to a spectrum of encoding patterns, ranging from stable to dynamic representations of the upcoming movement. Our results indicate that neural activity unfolds over multiple timescales during motor planning, suggesting a shared mechanism in the brain for processing temporal information related to both past memories and future plans.

neuroscience↗

bioRxiv2022

The time to initiate retrieval of a memory depends on recency

Continuous recognition has long been used to study the recency effect in recognition memory. In continuous recognition, response time (RT) increases as a logarithmic function of the lag since a probe was last presented. Although this could simply be due to decaying trace strength, careful examination of response time (RT) distributions showed that the onset of RT distributions changed with the logarithm of the lag since a probe was originally presented. Each doubling of lag resulted in a shift of roughly 20 ms in the rise time of the RT distributions. To test the hypothesis that this increase was simply due to increased facility in processing the probe item, Experiment six repeated items six times. Repetition resulted in faster RTs, but did not change the effect of log lag on RT. In light of recent neurophysio-logical evidence, we consider the hypothesis that memory requires a recovery of temporal context, and the time to retrieve a prior temporal context goes up with the logarithm of the time since it was experienced.

animal behavior and cognition↗

bioRxiv2019

A temporal record of the past with a spectrum of time constants in the monkey entorhinal cortex

Episodic memory is believed to be intimately related to our experience of the passage of time. Indeed, neurons in the hippocampus and other brain regions critical to episodic memory code for the passage of time at a range of time scales. The origin of this temporal signal, however, remains unclear. Here, we examined temporal responses in the entorhinal cortex of macaque monkeys as they viewed complex images. Many neurons in the entorhinal cortex were responsive to image onset, showing large deviations from baseline firing shortly after image onset but relaxing back to baseline at different rates. This range of relaxation rates allowed for the time since image onset to be decoded on the scale of seconds. Further, these neurons carried information about image content, suggesting that neurons in the entorhinal cortex carry information not only about when an event took place but also the identity of that event. Taken together, these findings suggest that the primate entorhinal cortex uses a spectrum of time constants to construct a temporal record of the past in support of episodic memory.

neuroscience↗