neurodudes

Modulation of intracortical synaptic potentials by presynaptic somatic membrane potential : Nature

Very interesting work. Modulation of the somatic potential seems to influence the EPSP, as measured by paired patch recordings of two layer 5 cells in cortical slice. Somatic depolarization from resting potential to near threshold results in an increase in evoked EPSPs.

In synaptic physiology, we often make a point of distinguishing intrinsic changes (eg. membrane potential) from synaptic conductance changes. Now it looks like the line between those might be a bit blurry!

Here’s a N&V by Eve Marder too.

Cell : Astrocytes Put down the Broom and Pick up the Baton [N&V summary]

Some beautiful work [original article] by Oliet’s lab in a recent issue of Cell demonstrates the importance of glia in synaptic plasticity. The show a system where D-serine and not glycine controls the NMDA receptor in a coagonist role (or perhaps glutamate is really the coagonist…) and show how similar pairing protocols can have opposite effects (LTD vs. LTP) depending on D-serine modulation by astrocytes. Yet more hidden factors in plasticity are being revealed!

Here’s the key figure:

More details from the News & Views summary after the jump. (more…)

Intelligent Life 2006 | From A to Zzzzz

Introducing CX717, a drug being developed by Cortex Pharmaceuticals of Irvine, California. It’s the first of what promises to be many aimed at detaching people from the daily routine of eight hours each for work, rest and play.

Tests conducted on rhesus monkeys last year suggest that CX717 can wire users to remain awake for 36 hours without the jitters, euphoria and eventual crash that come after mega-doses of caffeine or amphetamines. Further down the line are even more radical compounds—stimulants that can wipe out sleep for several days at a stretch, and pills that deliver a whole night’s shut-eye in two hours.

More information about the ampakine CX717 can be found here. We previously mentioned the delay match-to-sample performance improvement of monkeys on CX717.

Synaptic tuning : Nature Reviews Neuroscience

For those interested in neuromodulators:

Treatment of striatal neurons with a D1 receptor agonist led to an increase in the dendritic staining intensity of NMDA receptor NR2B subunits. There was also an increase in the association of NR2B subunits with PSD-95 — a scaffold protein required for the assembly of NMDA receptors — and in the surface localization of NR2B-containing receptors.

Original article in J. Neurosci. from Dunah and colleagues. An excerpt from the original aricle of a neat application of FRET continues after the jump.
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Two Coincidence Detectors for Spike Timing-Dependent Plasticity in Somatosensory Cortex — Bender et al. 26 (16): 4166 — Journal of Neuroscience

Dan Feldman’s group at UCSD has found that different “sides” of STDP (ie. LTP vs. LTD) at cortical synapses might be mediated through distinct signalling pathways. The major finding was that LTD was induced independent of NMDA receptors. Rather, LTD required mGluRs and VGCCs.

There are many questions here. The most interesting to think about is, Are we going to find different STDP rules all over the brain? And, if so, what will be the commond ground between them?

Here’s the abstract:

Many cortical synapses exhibit spike timing-dependent plasticity (STDP) in which the precise timing of presynaptic and postsynaptic spikes induces synaptic strengthening [long-term potentiation (LTP)] or weakening [long-term depression (LTD)]. Standard models posit a single, postsynaptic, NMDA receptor-based coincidence detector for LTP and LTD components of STDP. We show instead that STDP at layer 4 to layer 2/3 synapses in somatosensory (S1) cortex involves separate calcium sources and coincidence detection mechanisms for LTP and LTD. LTP showed classical NMDA receptor dependence. LTD was independent of postsynaptic NMDA receptors and instead required group I metabotropic glutamate receptors and calcium from voltage-sensitive channels and IP3 receptor-gated stores. Downstream of postsynaptic calcium, LTD required retrograde endocannabinoid signaling, leading to presynaptic LTD expression, and also required activation of apparently presynaptic NMDA receptors. These LTP and LTD mechanisms detected firing coincidence on ~25 and ~125 ms time scales, respectively, and combined to implement the overall STDP rule. These findings indicate that STDP is not a unitary process and suggest that endocannabinoid-dependent LTD may be relevant to cortical map plasticity.

Last year, the Redwood Center for Theoretical Neuroscience moved from the Redwood Neuroscience Institute in Meno Park to the Helen Wills Neuroscience Institute at Berkeley. In October they held a symposium with several interesting speakers presenting on various topics within Theoretical Neuroscience.

The videos are now online for your perusal, or you can buy a DVD of the whole symposium for a paltry $5.

• Horace Barlow, Cambridge University: The Roles of Theory, Commonsense, and Guesswork in Neuroscience
• Dan Kersten, University of Minnesota: Human Object Perception: Theory, Psychophysics & Imaging
• Sue Becker, McMaster University: The role of the hippocampus in memory, contextual gating, stress and depression
• Florentin Worgotter, University of Goettingen: Learning in Neurons and Robots
• Panel Discussion: The Role and Future Prospects for Math/Computational Theories in Neuroscience
• David Heeger, New York University: What fMRI Can Tell Us about How Visual Cortex Works
• Kevan Martin, ETH/UNI Zurich: Canonical Circuits for Neocortex
• Terry Sejnowski, Salk Institute: Dendritic Darwinism
• Jeff Hawkins, Numenta: Prospects and Problems of Cortical Theory

A forthcoming issue of the journal Neuroscience is devoted to an examination of multidisciplinary approaches to the study of working memory within the field of Cognitive Neuroscience. Although the issue will not be released until late April, a detailed press release is available from the University of Washington at St. Louis.

From the article:

“Multidisciplinary research within cognitive neuroscience has established itself as a promising approach to answering the question of how the mind emerges from the working of the brain” [...] “One of the fields that has gained substantially by successfully combining the theoretical frameworks, methodologies, empirical results and insights of the varied disciplines within cognitive neuroscience, is the study of working memory”

It goes on to describe a “pyramid approach” to multidisciplinary work in this area, which chiefly involves the merging of cognitive psychology, computational science, neuroscience, and cognitive neuropsychiatry.

What gives humans the unique ability to construct novel sentences from the building blocks of language? A recent article in Behavioral and Brain Sciences proposes a “neural blackboard architecture” is capable of just this.

From the article (doi: 10.1017/S0140525X06009022):

“This paper aims to show that neural “blackboard” architectures can provide an adequate theoretical basis for a neural instantiation of combinatorial cognitive structures. [...] We also discuss the similarities between the neural blackboard architecture of sentence structure and neural blackboard architectures of combinatorial structures in visual cognition and visual working memory [...]”

As with all main articles in Behavioral and Brain Sciences, this one is followed by extensive comment and criticism from colleagues, and finally a reply by the authors. This provides a very deep look at the article and the issues surrounding it.

An older, but freely available, version of the article is available here.

PLoS Biology: Attenuation of Self-Generated Tactile Sensations Is Predictive, not Postdictive [open access]

I haven’t gotten a chance to fully digest this article (What is the attenuation phenomena that happens when the taps are delayed?), but it seems like a deep result from a relatively simple haptics experiment. Just thought I’d share it with the crowd.

Also, Happy Birthday to fellow Neurodude Bayle! Congrats, man.

“Scans of brain activity, published online in the journal Nature Neuroscience, indicate that the brain can actually get into the ‘right frame of mind’ to store new information and that we perform at our best if the brain is active not only at the moment we get new information but also in the seconds before.
….
Tests showed that the brain’s electrical activity differed after the cue question and before the word was presented and this was linked to whether the subject would remember or forget the word in a later unexpected memory test. If the electrical activity maintained a high level over frontal parts of the scalp just before the word was shown, then it was likely that the subject would remember the word up to 50 minutes later – and after doing a series of other word tests. On the other hand, if the voltage was lower, the subjects were less likely to remember the word.”

(from the press release)

Leun J. Otten, Richard N. A. Henson & Michael D. Rugg. State-related and item-related neural correlates of successful memory encoding. Nature Neuroscience 5, 1339 – 1344 (2002). Published online: 28 October 2002; doi:10.1038/nn967