One person’s (John Lisman) take on the state of the art of neuroscience in 2015.
The Challenge of Understanding the Brain: Where We Stand in 2015
Frontiers for Young Minds is edited by kids 8 to 18. Best quote: ““Woe betide the contributor who falls under my editorial pen,” wrote 14-year-old Caleb from Canada.
Michale Fee and crew review and synthesize three major models of basal ganglia output (disinhibition, rebound, and entrainment).
Pesenson, Cohen, and Voytek review methods for linking nonlinear oscillatory neural dynamics, in particular oscillatory phase, to behavior.
Linking Nonlinear Neural Dynamics to Single-Trial Human Behavior
Kraus et al required rats to run on a treadmill during a working memory task. They dissociated distance traveled vs time spent running by requiring the rats to run for a fixed distance or a fixed amount of time. This revealed “time cells” in the hippocampus that reflect the passage of time.
It was recently reported that low-voltage, non-invasive brain stimulation improves mathematical abilities. Does it? Here’s a cautionary discussion:
Does Brain Stimulation Make You Better at Maths?
Visual attention modulates several aspects of neural coding. There is an increase in firing rate and changes in temporal dynamics: a reduction of neural variance and noise correlation as well as changes in oscillatory synchronization. The authors used glutamatergic receptor activation, combined with neurophysiological recording to show that the NMDA receptor is responsible for attention -related changes in neural temporal dynamics but not for increases in firing rate. Thus, different neurophysiological mechanisms that underlie attention can be dissociated at the receptor level. This supports the hypothesis that attention is mediated in part by the temporal dynamics of neural activity, not merely changes in the firing rate of neurons, and that the changes temporal dynamics are not simply a byproduct of changes in firing rate.
Herrero et al (2013) Neuron
For a further discussion of the role of temporal dynamics in attention see:
Miller, E.K. and Buschman, T.J. (2013) Cortical circuits for the control of attention. Current Opinion in Neurobiology. 23:216–222 View PDF »
Buschman, T.J. and Miller, E.K. (2007) Top-down versus bottom-up control of attention in the prefrontal and posterior parietal cortices. Science. 315: 1860-1862 . View PDF »
Buschman, T.J. and Miller, E.K. (2009) Serial, covert, shifts of attention during visual search are reflected by the frontal eye fields and correlated with population oscillations. Neuron, 63: 386-396. View PDF »
In this week’s NY Times, Susana Martinez-Conde reminds us that our visual system works by detecting change.
http://www.nytimes.com/2013/05/19/opinion/sunday/vision-is-all-about-change.html
The title says it all. Oscillations are useful for all sorts of things.
Synchrony in 32 metronomes
Rhythmic synchrony between neurons has been suggested as a mechanism for establishing communication channels between neurons. However, this hypothesis has been criticized because of observations that the exact frequency of gamma oscillations bounces around too much to provide a stable communication channel. (BTW, it doesn’t seem to bother anyone that single neuron activity also bounces around).
In this study, Roberts et al record from V1 and V2 simultaneously while presenting gratings of varying contrast. Even though the gamma frequencies changed with stimulus contrast and fluctuated over time, coherence remained stable between V1 and V2. Thus, rhythmic synchrony can provide a stable channel for neural communication.
http://www.cell.com/neuron/abstract/S0896-6273(13)00227-4?utm_source=feedly
For further reading on the role of rhythmic synchrony in neural communication see:
Miller, E.K. and Buschman, T.J. (2013) Cortical circuits for the control of attention. Current Opinion in Neurobiology. 23:216–222 View PDF »
Buschman, T.J., Denovellis, E.L., Diogo, C., Bullock, D. and Miller, E.K. (2012) Synchronous oscillatory neural ensembles for rules in the prefrontal cortex. Neuron, 76: 838-846. View PDF
Our very limited ability to hold multiple thoughts in mind is apparent to anyone who has tried to talk on the phone and email at the same time. Traditionally, this is thought of as a limitation in the capacity of working memory, the “mental scratchpad” used to keep important information “online” after it is no longer available. However, Ed Vogel and crew show that the bottleneck is not in working memory per se but instead present during processing of visual stimuli while they are still visible. Thus, the bottleneck is not (just) in memory but also in the processing of sensory inputs. In other words, capacity limitations seem to be a fundamental limit in neural processing related to consciousness in general, not a unique byproduct of working memory.
http://www.jneurosci.org/content/33/19/8257.abstract
As noted by the authors, this is consistent with our finding that when capacity is exceeded, information is lost in a bottom-up fashion during initial processing of visual stimuli:
Buschman,T.J., Siegel, M., Roy, J.E. and Miller, E.K. (2011) Neural substrates of cognitive capacity limitations. Proceedings of the National Academy of Sciences. 108(27):11252-5. View PDF »
Miller Lab Research Scientist Vicky Puig quoted in a article in El Pais. The Picower Institute at MIT is called “one of the best neuroscience centers in the world”. One of the?
In Spanish, but that’s why we have Google Translate.
http://elpais.com/elpais/2013/05/01/eps/1367419412_106866.html