Inbal Goshen, Matthew Brodsky, Rohit Prakash, Jenelle Wallace, Viviana Gradinaru, Charu Ramakrishnan, Karl Deisseroth. Dynamics of Retrieval Strategies for Remote Memories. Cell, Volume 147, Issue 3, 28 October 2011, Pages 678-689.

Prevailing theory suggests that long-term memories are encoded via a two-phase process requiring early involvement of the hippocampus followed by the neocortex. Contextual fear memories in rodents rely on the hippocampus immediately following training but are unaffected by hippocampal lesions or pharmacological inhibition weeks later. With fast optogenetic methods, we examine the real-time contribution of hippocampal CA1 excitatory neurons to remote memory and find that contextual fear memory recall, even weeks after training, can be reversibly abolished by temporally precise optogenetic inhibition of CA1. When this inhibition is extended to match the typical time course of pharmacological inhibition, remote hippocampus dependence converts to hippocampus independence, suggesting that long-term memory retrieval normally depends on the hippocampus but can adaptively shift to alternate structures. Further revealing the plasticity of mechanisms required for memory recall, we confirm the remote-timescale importance of the anterior cingulate cortex (ACC) and implicate CA1 in ACC recruitment for remote recall.

Scientists use brain imaging to reveal the movies in our mind.

In a delayed-nonmatch-to-sample task, a rat was shown one of two levers, then there was a delay during which the rat was distracted, then the rat was shown both levers and was supposed to press the one it hadn’t been shown at first. The model of CA1 was trained on the most difficult, successful trials, then replayed later to stimulate CA1.

Stimulation occurred in two conditions: normal, and when glutamate transmission was blocked. In both conditions, the prosthesis augmented performance by about 20%. I couldn’t tell from the paper whether they had different models depending on which lever was about to be pressed, and chose to play the correct model to stimulate recall; if they did, then this is really just showing that the prosthesis can affect which memory is recalled, not that it can actually substitute for CA1.

Theodore W Berger, Robert E Hampson, Dong Song, Anushka Goonawardena, Vasilis Z Marmarelis and Sam A Deadwyler. A cortical neural prosthesis for restoring and enhancing memory. 2011 J. Neural Eng. 8 046017

We blogged about this project a few years ago: http://neurodudes.com/2007/04/04/interview-on-usc-hippocampal-prosthetic/

MAPPING MULTISENSORY REPRESENTATIONS OF PERIPERSONAL SPACE

Ruey-Song Huang

Swartz Center for Computational Neuroscience, Institute for Neural Computation, and Department of Cognitive Science

http://sccn.ucsd.edu/~rshuang/

This talk will present our recent progress in mapping multisensory representations of peripersonal space using fMRI, with topics covering both technical developments and scientific findings. Recently, we have developed wearable techniques for high-density and/or wide-range tactile stimulation in the MRI scanner. Sixty-four channels (expandable to 128) of computer-controlled air puffs can be delivered via plastic tubes/nozzles embedded in the air suit, including the face mask, turtleneck, gloves, and pants. The wearable techniques open the possibilities of presenting more complex tactile stimuli with programmable spatial-temporal patterns on the body surface, e.g. 2-D tactile display or tactile apparent motion.

Multiple two-condition block-design scans revealed a high-level somatotopic homunculus consisting of the parietal face, lip, finger, and shoulder areas in the superior parietal lobe. Retinotopic mapping using phase-encoded design and wide-field visual stimuli (masked videos or looming objects) further revealed aligned visual-tactile maps in the same areas. Tactile mapping revealed a high-level homunculus consisting of the parietal face, lip, finger, and shoulder areas in superior parietal lobule. Visual mapping revealed an aligned visual homunculus in the same areas. A region of lower visual field representation in the post-central sulcus partially overlaps with the parietal finger area, which is anterior and lateral to the parietal face/lip areas. Another region of lower visual field representation, superior and medial to the parietal face area, partially overlaps with the parietal shoulder area. However, regions of upper visual field representation were restricted to the parietal face area. We suggest that aligned multisensory homunculi may play important roles in combining visual and tactile information to facilitate movements in the peripersonal space (e.g., eating involves hand-to-mouth coordination in the lower visual field).

Ho Ko, Sonja B. Hofer, Bruno Pichler, Katherine A. Buchanan, P. Jesper Sjöström, Thomas D. Mrsic-Flogel. Functional specificity of local synaptic connections in neocortical networks. Nature. 2011 May 5;473(7345):87-91. Epub 2011 Apr 10.

By way of Nextbigfuture, by way of Hackernews.

However, because it can only go down so far, the negative signal is clipped, which might have consequences (see Yael Niv, Michael O Duff, Peter Dayan. Dopamine, uncertainty and TD learning).

The previous article mentions that some other people think that maybe dopamine is tracking uncertainty as well as reward. This one talks about a theory that acetylcholine is related to expected uncertainty, and norepinephrine is related to unexpected uncertainty:
Angela Yu, Peter Dayan. Expected and Unexpected Uncertainty: ACh and NE in the Neocortex (huh, all those papers had Peter Dayan as one of the authors) (btw I haven’t read all of the papers I’m posting here)

Since we’re on the subject of temporal difference learning, I’ll mention that in my opinion temporal difference learning may be a model of how futures/speculators in financial markets are supposed to propagate future price changes back in time to the present (if you think of the market as a cognitive system). I haven’t formalized this idea yet, though.

(1) when rats are sleep-deprived, small populations of rat brain neurons can fall asleep while the rest of the rat is awake, and
(2) this may correspond to performance degradation

summary:
http://arstechnica.com/science/news/2011/04/if-you-only-feel-half-awake-you-probably-are.ars

article:

http://www.nature.com/nature/journal/v472/n7344/full/nature10009.html

i haven’t read the actual article yet…

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature09817.html

Abstract after the break.

Adult hippocampal neurogenesis is a unique form of neural circuit plasticity that results in the generation of new neurons in the dentate gyrus throughout life. Neurons that arise in adults (adult-born neurons) show heightened synaptic plasticity during their maturation and can account for up to ten per cent of the entire granule cell population. Moreover, levels of adult hippocampal neurogenesis are increased by interventions that are associated with beneficial effects on cognition and mood, such as learning, environmental enrichment, exercise and chronic treatment with antidepressants. Together, these properties of adult neurogenesis indicate that this process could be harnessed to improve hippocampal functions. However, despite a substantial number of studies demonstrating that adult-born neurons are necessary for mediating specific cognitive functions, as well as some of the behavioural effects of antidepressants, it is unknown whether an increase in adult hippocampal neurogenesis is sufficient to improve cognition and mood. Here we show that inducible genetic expansion of the population of adult-born neurons through enhancing their survival improves performance in a specific cognitive task in which two similar contexts need to be distinguished. Mice with increased adult hippocampal neurogenesis show normal object recognition, spatial learning, contextual fear conditioning and extinction learning but are more efficient in differentiating between overlapping contextual representations, which is indicative of enhanced pattern separation. Furthermore, stimulation of adult hippocampal neurogenesis, when combined with an intervention such as voluntary exercise, produces a robust increase in exploratory behaviour. However, increasing adult hippocampal neurogenesis alone does not produce a behavioural response like that induced by anxiolytic agents or antidepressants. Together, our findings suggest that strategies that are designed to increase adult hippocampal neurogenesis specifically, by targeting the cell death of adult-born neurons or by other mechanisms, may have therapeutic potential for reversing impairments in pattern separation and dentate gyrus dysfunction such as those seen during normal ageing.

“Google’s worldwide Science Fair competition …is calling for entries over the next few days. It gives kids the opportunity to join in a new kind of online science competition…offering them the chance to win … prizes including a 10-day trip to the Galapagos Islands or a $50,000 scholarship.”

They paid us to post this video of a Rube Goldberg machine (you don’t need sound, it’s just random music):

(you won’t be able to see it if you have AdBlock enabled)