A (very brief) mention of the new paper by Antzoulatos and Miller (2014) on National Public Radio.
The paper:
Antzoulatos, E.G. and Miller, E.K. (in press) “Increases in functional connectivity between the prefrontal cortex and striatum during category learning.” Neuron. View PDF
Antzoulatos EG and Miller EK (in press) Increases in Functional Connectivity between Prefrontal Cortex and Striatum during Category Learning. Neuron, in press.
DOI: http://dx.doi.org/10.1016/j.neuron.2014.05.005
Animals were trained to learn new category groupings by trial and error. Once they started to “get” the categories, there was an increase in beta-band synchrony between the prefrontal cortex and striatum, two brain areas critical for learning. By the time the categories were well-learned, the beta synchrony between the areas became category-specific, that is, unique sets of sites in the prefrontal cortex and striatum showed increased beta synchrony for the two different categories. This suggests that synchronization of brain rhythms can quickly establish new functional brain circuits and thus support cognitive flexibility, a hallmark of intelligence.
MIT Press release:
Synchronized brain waves enable rapid learning
MIT study finds neurons that hum together encode new information.
Matsushima and Tanaka compared neural correlates of spatial working memory for locations within the same hemifield or across hemifields. When the two remembered locations were in the same hemifield (right or left side of vision), the neural response in the prefrontal cortex was intermediate to the two cues presented alone. When the cues were across hemifields, the neural response was the same as the preferred cue presented alone. In other words, remembered locations within a hemifield seemed to be in competition with each other whereas locations across the hemifields seemed to be have no interaction at all. In yet other words, it was as if the (intact) monkeys had their brains split down the middle. The authors concluded local inhibitory interactions between cues within, but not across, hemifields.
This confirms Buschman et al (2011) who found that independent capacities for visual working memory in the right and left hemifields.
Further reading:
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 »
Does the prefrontal cortex (PFC) maintain the contents of working memory or does it direct the focus of attention? Lara and Wallis asked this question by training monkeys to perform a multi-color change detection task. Few PFC neurons encoded the color of the stimuli. Instead, the dominant signals were the spatial location of the item and the location of focal attention. This suggests that the PFC is more involved in directing attention than retaining information in working memory. Supporting this was increased power in alpha and theta power in the PFC, frequency bands associated with long-range neural communication.
Tirin Moore and colleagues challenge the idea that neuron receptive fields shift in anticipation of eye movements, remapping from the pre-movement location to the post-movement location before the eye actually moves. They used multiple-electrode recording to provide a detailed maps of the receptive fields before and after movements. The receptive fields did not remap to reflect the post-movement location. Instead, all the receptive fields converged toward movement target. This suggest that the receptive field do not remap, they reflect attention to the movement target.
Recent studies have suggested that beta-band oscillatory synchrony plays a role in cognition. For example, different networks of neurons in the prefrontal cortex dynamically synchronize at beta as animals switch between two different task rules (Buschman et al., 2012) suggesting that beta synchrony is forming the neural ensembles for the rules. Different items simultaneously held in working memory line-up on different phases of beta/low-gamma oscillations, as if the brain is juggling the two items 30 times a second (Siegel et al., 2009). Hanslmayr et al disrupted these fine temporal relations by stimulating the human with beta-band TMS pulses. Beta stimulation of the left inferior frontal gyrus impaired memory formation while stimulation at other frequencies did not. There was a beta “echo” that outlasted the stimulation. Subjects with better beta entrainment showed more memory impairment. This lends support for the role of beta rhythms in cognition by showing a causal relationship between beta desynchrony and memory.
This paper:
Simon Hanslmayr, Jonas Matuschek, Marie-Christin Fellner, Entrainment of Prefrontal Beta Oscillations Induces an Endogenous Echo and Impairs Memory Formation, Current Biology, Available online 27 March 2014, ISSN 0960-9822
References
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
Siegel, M., Warden, M.R., and Miller, E.K. (2009) Phase-dependent neuronal coding of objects in short-term memory. Proceedings of the National Academy of Sciences, 106: 21341-21346. View PDF » Read commentary by Vogel and Fukuda
Think you can multitask well? Watanabe and Funahasi show that task information signaled by neurons in the prefrontal cortex degrade when animals perform a competing, concurrent task.
An excellent review by Matt Shapiro and crew on an important topic. They discuss complementary roles and bidirectional interactions between the prefrontal cortex and hippocampus.
Noudoost, Clark, and Moore deactivated the frontal eye fields (FEF) and recorded from visual cortical area V4. This disrupted saccades to targets but *increased* pre-saccade activity in V4. V4 neurons, however, showed reduced discrimination of the target stimulus. It seems that the FEF provides details about the saccade target to visual cortex.
Genovesio et al trained monkeys to judge whether red square or blue circle were farther from a reference point. Even though information about the previous trial was irrelevant to the current trial, prefrontal cortex neurons conveyed the outcome of the previous trial and other irrelevant information about it. Information about previous outcomes can often be helpful. This study shows that this is automatically tracked by the prefrontal cortex even when it is not helpful.