"The present contains nothing more than the past, and what is found in the effect was already in the cause", Henri L. Bergson

Working Memory & its Multiple 

Timescales

Memory is a key building block of cognition. Whether it’s short as remembering a phone number before dialing it, or long as rules of playing chess, the brain is constantly engaged in storing new memories and executing actions while integrating sensory information with past memories and subject’s internal model of the task. Working memory (WM), the ability to store and manipulate information for short periods of time, is an example where contextual information becomes an integral part of perception and memory. Despite extensive research, mechanisms underlying WM have remained obscure. A particular type of WM task, called Parametric Working Memory (PWM), is delayed comparison, the sequential comparison of two graded stimuli separated by a delay period of a few seconds, which forces the subject to maintain an analog value in memory. An identifying feature of PWM is that it is adaptive to various factors in the task, e.g the saliency of the stimuli, the delay duration, and task history.

During my time at Diamond lab, we developed the first Parametric Working Memory (PWM) task in rats (4). Over the past couple of decades, primates have been the focus of research on neural correlates of PWM. Compared to the primate nervous system, that of rodents is more amenable to visualization and external manipulations. Additionally, a larger numbers of subjects can be studied with lower cost. However, PWM paradigms were assumed impossible in rodents due to the difficulty of training protocols. My comparative human psychophysics experiments showed that rats’ PWM capacities are remarkably similar to humans’ (1, 4).

During my postdoctoral research in Brody lab, I expanded the rodent PWM task to the auditory domain, using semi-automated training protocols implemented in high-throughput training facilities. I also developed several computational methods to assay PWM behavior and its interplay with prior sensory history in rats and humans. Further, I combined formal algorithmic behavioral analysis, optogenetic inactivations, and electrophysiological recordings in rats to show that Posterior Parietal Cortex (PPC) is specifically involved in the representation and use of prior sensory experience in PWM (1)

See here the Nature News and Views piece by Prof. Laura Busse on our paper:

 

Working memory freed from the past

And see here the Neuron Spotlight piece by Prof. Miguel Maravall et al on our paper:

Cortical Lifelogging: The Posterior Parietal Cortex as Sensory History Buffer

  1. Athena Akrami, Charles Kopec, Mathew Diamond Carlos Brody. “Posterior parietal cortex represents sensory history and mediates its effects on behavior", Nature 2018 (BioRxiv version)
  2. Arash Fassihi, Athena Akrami, Vinzenz Schoenfelder, Francesca Pulecchi, Mathew Diamond. “Transformation of Perception from Sensory to Motor Cortex”. (Current Biology, 2017).

  3. Ji Hyun Bak, Jung Yoon Choi, Athena Akrami, Witten Ilana, & Pillow Janathan. “Adaptive optimal training of animal behavior”, Advances in Neural Information Processing Systems 29 (NIPS, 2016)

  4. Arash Fassihi*, Athena Akrami*, Vahid Esmaeili, Mathew E. Diamond, “Tactile perception and working memory in rats and humans”, (PNAS 2014, *equal co-first author)

  5. Arash Fassihi, Athena Akrami, Vahid Esmaeili, Fabrizio Manzino and Mathew E. Diamond, "Sensation of a noisy whisker vibration in rats”, Living Machines 2012, LNAI 7375 proceedings

Attractors, Memory 

& Perception

  1. Athena Akrami, Eleonora Russo, Alessandro Treves, “Lateral thinking, from the Hopfield model to cortical dynamics”, Brain Research, July 2011

  2. Athena Akrami, Alessandro Treves, “Neural basis of perceptual expectations: insights from transient dynamics of attractor neural networks”, BMC Neuroscience 2009, 10(Suppl 1):P174

  3. Athena Akrami, Yan Liu, Alessandro Treves and Bharathi Jagadeesh, “Converging neuronal activity in inferior temporal cortex during the classification of ‘morphed’ stimuli”, Cerebral Cortex, 2009 April; 19(4): 760-76

During my graduate work in Alessandro Treves’ group at SISSA (Trieste, Italy), I developed a theoretical framework to evaluate the contributions of attractor dynamics to the perception of ambiguous stimuli (1, 2, 3)

Aiming to explore the neural basis of attractor dynamics in visual cortex, we have recorded from IT cortex in two monkeys while the animal was presented with morphed visual stimuli. The neural data is suggestive of a possible contribution of attractor dynamics in producing categorical boundaries. This hypothesis, together with another alternative one (firing rate adaptation) was then tested, by

simulating a simple autoassociative network model, and found to be consistent with observations (3). 

I showed that the same type of model is also able to describe the transient dynamics involved in some well-known behavioral traits in humans, including the adaptation aftereffect and priming. This suggests that common neural processes may underlie these phenomena, which were previously considered to be distinct (2).

Hippocampus, Memory

& Perception

  1. Natalia Grion*, Athena Akrami*, Yangfang Zuo, Federico Stella, Mathew E. Diamond, “Coherence between rat sensorimotor system and hippocampus is enhanced during tactile discrimination” (PLoS Biology 2016, *equal co-first author)​

  2. Athena Akrami, Pavel Itskov, Mathew E. Diamond, “Hippocampal population dynamics underlying memory trace activation in a tactile classification task”, BMC Neuroscience 2011, 10(Suppl 1):P70

In rats, the hippocampus and the vibrissal sensorimotor system (whisking) are both characterized by rhythmic oscillation in the theta range (5-12 Hz). Previous work had been divided as to whether the rhythms of the two systems are independent or coherent; the most recent inquiry argued for independence. Our hypothesis was that the sensorimotor system and hippocampus become coherent selectively in moments when the hippocampus must integrate tactile information into memory networks. Barrel cortex e exhibits rhythmic neuronal activity during vibrissa-based sensation.

 

In Diamond's lab, we showed that this activity transiently locks to ongoing hippocampal theta-rhythmic activity during the sensory-gathering epoch of a discrimination task. These results suggest that, as rats collect touch signals, enhanced coherence between the whisking rhythm, sensory cortex, and hippocampal local field potential (LFP) boosts the efficiency of integration of sensory information into memory and decision making centers.

Image by Moritz von Heimendahl and Marco Gigante