A study on electrophysiological recordings from single neurons in the dorsolateral prefrontal cortex of two monkeys trained to perform a visual target discrimination task (Lennert & Martinez-Trujillo, 2011) has supposedly given new hope to patients with a diverse array of neurological and psychiatric conditions, according to a press release:
Filters That Reduce ‘brain Clutter’ IdentifiedI am so flabbergasted by the number of misleading statements that I don't know where to begin. Let's take them in the order of occurrence.
ScienceDaily (Apr. 19, 2011) — Until now, it has been assumed that people with conditions like ADHD, Tourette syndrome, obsessive compulsive disorder and schizophrenia -- all of whom characteristically report symptoms of "brain clutter" -- may suffer from anomalies in the brain's prefrontal cortex.Damage to this brain region is often associated with failure to focus on relevant things, loss of inhibitions, impulsivity and various kinds of inappropriate behaviour. So far, exactly what makes the prefrontal cortex so essential to these aspects of behaviour has remained elusive, hampering attempts to develop tools for diagnosing and treating these patients.But new research by Julio Martinez-Trujillo, a professor in McGill University's Department of Physiology and Canada Research Chair in Visual Neuroscience, has brought new hope to these patients. He believes the key to the "brain clutter" and impulsivity shown by individuals with dysfunctional prefrontal cortices lies in a malfunction of a specific type of brain cell. Martinez-Trujilo and his team have identified neurons in the dorsolateral sub-region of the primate prefrontal cortex that selectively filter out important from unimportant visual information. The key to the normal functioning of these "filter neurons" is their ability to, in the presence of visual clutter, selectively and strongly inhibit the unimportant information, giving the rest of the brain access to what is relevant.
- "Until now" - This phrase implies that the study has refuted the assumption that ADHD, Tourette's, OCD, and schizophrenia are all associated with abnormalities in the prefrontal cortex (PFC). In fact, individuals with these disorders (and their PFCs) were not evaluated.
- "brain clutter" - What does this mean? I'm not familiar with it as a technical term, nor how the phenomenon is manifest in all four of the above disorders. This issue is relatively minor.
- "anomalies in the brain's prefrontal cortex" - The human PFC covers a large and diverse area of the brain.
Fig. 1 (Fuster, 2002). Three views of the cerebral hemispheres with the areas of the prefrontal cortex numbered in accord with Brodmann’s cytoarcitectonic map.
- Neuroimaging findings in ADHD, Tourette's, OCD and schizophenia are not uniform, and the implicated subregions of PFC are not the same. For example, OCD has been associated with overactivity in the orbitofrontal cortex (Menzies et al., 2008) while schizophrenia is associated with altered activation of dorsolateral PFC (Volk & Lewis, 2010).1
- This is highly relevant because as we'll see, the monkey neurons under investigation were in a specific region analogous to Brodmann area 46 in human dorsolateral PFC.
- "Damage to this brain region" and the subsequent laundry list of altered behaviors - not all associated with damage to BA 46.
- "brought new hope to these patients" - This is by far the most egregious falsehood of the entire press release. I find it to be utterly irresponsible.
None of these claims were made in the paper itself, which examined firing rates of neurons in the principal sulcus of two rhesus macaque monkeys trained to perform a color-rank target discrimination task with moving random dot patterns.
Figure adapted from the press release. The pinkish highlighted area of the brain is the principal sulcus region where neuron activity was recorded.
The authors summarize the results below. You'll notice there's no mention of developing "tools for diagnosing and treating these patients" or bringing "new hope to these patients."
Here's the link for the original press release from McGill University. If you are so inclined:
► Interstimulus ordinal distance modulates attentional-filtering strength in monkeys ► Interstimulus ordinal distance modulates target selection by prefrontal neurons ► Varying suppression of distracters by dlPFC neurons determines attentional filtering ► Target enhancement by dlPFC neurons remains invariable with changes in performance
- Katherine Gombay, Media Relations Office, McGill University - Tel.: 514 398-2189
1 I'm skipping the complexities of multiple fronto-striato-thalamic circuits.
Fuster JM. (2002). Frontal lobe and cognitive development. J Neurocytol. 31:373-85.
Lennert, T., & Martinez-Trujillo, J. (2011). Strength of Response Suppression to Distracter Stimuli Determines Attentional-Filtering Performance in Primate Prefrontal Neurons Neuron, 70 (1), 141-152 DOI: 10.1016/j.neuron.2011.02.041
Menzies L, Chamberlain SR, Laird AR, Thelen SM, Sahakian BJ, Bullmore ET. (2008). Integrating evidence from neuroimaging and neuropsychological studies of obsessive-compulsive disorder: the orbitofronto-striatal model revisited. Neurosci Biobehav Rev. 32:525-49.
Volk DW, Lewis DA. (2010). Prefrontal cortical circuits in schizophrenia. Curr Top Behav Neurosci. 4:485-508.
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