neurodudes

Transcranial magnetic stimulation (TMS) is a popular technology for stimulating human cortical neurons, due to its safety, noninvasiveness, and efficacy. A TMS device is just a little coil of wire, through which 10,000 Amps of current is cranked during a period of only a few hundred microseconds; the resultant rapidly-changing magnetic field induces eddy currents in the brain. Depending on the protocol used, TMS can drive/inhibit a region of cortex corresponding to roughly a cubic centimeter or two, and is being explored for the treatment of depression, the reduction of auditory hallucinations during schizophrenia, and the alleviation of tinnitus and migraines. Thousands of papers on medicine and psychology have been written using this tool.

Yet the device itself is expensive and rare — they can run from $20,000 to $50,000 or even more, despite the fact that they are, in essence, a coil, a switch, a bank of capacitors, and a power supply. Much of the art lies in making the devices safe and fail-proof. Is it possible to hack/engineer a system that is safe, fault-tolerant, efficacious, and inexpensive? And furthermore, can we facilitate a community that will devise such devices, and share information about protocols and approaches to brain hacking?

This past August at Foo Camp, a hackers’ conference in Northern California, a group of people got together and set out to do just that. We are designing a safe, noninvasive, modular, and “open source” brain stimulator that will open up the field of circuit modulation to a wider audience. Members of the group include therapists and mental health professionals, engineers, programmers, and others interested in either the development of such devices, or the sharing of information on this front. Key to the design is safety — we want to make sure that the devices we create are as safe as devices on the market. Also, all the information is released under the Creative Commons “Attribution and Sharealike” license. This is a new model for “open source” medical device development — which may move it beyond the domain of simply creating “cool toys,” and to creating real devices.

You can find out more information, or contribute to the project, or learn from the project, at
http://transcenmentalism.org/OpenStim/

-Ed

It seems Markram is again back to getting some interesting results. Recently a new discovery from the Brain Mind Institute of the EPFL shows that the brain adapts to new experience by unleashing a burst of new neuronal connections, and only the fittest survive. The research further shows that this process of creation, testing, and reconfiguring of brain circuits takes place on a scale of just hours, suggesting that the brain is evolving considerably even during the course of a single day.

The paper can be found Here.

A very nice neuroecon expt. in the newest Nature:

Daw et al. find that humans choose between multiple slot machines (with different payoff probabilities) based on expected value (versus just going with the highest probability one most of the time and then randomly choosing another one every so often). Then, with fMRI, they find brain areas correlated with different value predictions.

News & Views (Daeyol Lee)

Cortical substrates for exploratory decisions in humans (Daw, Dayan)

Abstract:

Decision making in an uncertain environment poses a conflict between the opposing demands of gathering and exploiting information. In a classic illustration of this ‘exploration-exploitation’ dilemma, a gambler choosing between multiple slot machines balances the desire to select what seems, on the basis of accumulated experience, the richest option, against the desire to choose a less familiar option that might turn out more advantageous (and thereby provide information for improving future decisions). Far from representing idle curiosity, such exploration is often critical for organisms to discover how best to harvest resources such as food and water. In appetitive choice, substantial experimental evidence, underpinned by computational reinforcement learning (RL) theory, indicates that a dopaminergic, striatal and medial prefrontal network mediates learning to exploit. In contrast, although exploration has been well studied from both theoretical and ethological perspectives, its neural substrates are much less clear. Here we show, in a gambling task, that human subjects’ choices can be characterized by a computationally well-regarded strategy for addressing the explore/exploit dilemma. Furthermore, using this characterization to classify decisions as exploratory or exploitative, we employ functional magnetic resonance imaging to show that the frontopolar cortex and intraparietal sulcus are preferentially active during exploratory decisions. In contrast, regions of striatum and ventromedial prefrontal cortex exhibit activity characteristic of an involvement in value-based exploitative decision making. The results suggest a model of action selection under uncertainty that involves switching between exploratory and exploitative behavioural modes, and provide a computationally precise characterization of the contribution of key decision-related brain systems to each of these functions.

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.
(more…)

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.