brain – Page 4 – Brainy Behavior

November 2, 2007November 2, 2007

The neuroscience of aging

I’ll start with the bad news first. The human brain reaches it’s physical peak around the age of 25. After that it’s all downhill. The prefrontal cortex and underlying white matter is the last area of the brain to develop (including myelination); that area is also the first to start the decline. Myelination of the frontal cortex typically isn’t completed until the early to mid 20s. Its slow degradation starts quickly after it finishes development. This slow degradation of the brain correlates with slowed processing speed initially and, later in life, with declines in all areas of cognition. The good news is that cognitive performance in most areas does not typically decline until the mid 50s; many abilities such as verbal continue to increase until the mid 50s or early 60s. While there is often global brain matter loss (slowly over the decades), specific areas of the brain change at different rates (with some areas exhibiting volume increases until the mid 50s or so).

This news can be discouraging for people who are older than 25 (such as myself) – knowing that I am on the downward slope, at least as far as brain volume, myelination, and processing speed are concerned. I wrote about the bad news first so now the good news. Even though cognitive performance starts to decline, on average, in the mid 50s, many domains increase between age 25 and age 55; thus, the declines in late life often merely bring cognitive performance back down to where it was in the mid 20s. Of course processing speed in late life is a lot lower than in the early 20s but verbal memory and abilities, reasoning, and spatial abilities are quite intact in late life. Math abilities tend to decrease significantly over life though. The graph shows cognitive performance as measured by a 35-year longitudinal study (actually a sequential research design – both cross-sectional and longitudinal) (Schaie, K. W. Intellectual Development in Adulthood: The Seattle Longitudinal Study. Cambridge Univ. Press, Cambridge, 1996). Cognition across the lifespan

For a comprehensive review of cognitive and neurological changes associated with aging read Trey Hedden and John D. E. Gabrieli’s Nature Review: Neuroscience article published in February 2004. I’ve included a link to a PDF of the article: Aging article.

October 31, 2007October 31, 2007

Another anatomy site

I found a nice but very basic anatomy site (i.e., good for kids). It also has more anatomy than just the brain, with skeletal, heart, and digestive tract anatomy in English and Spanish.

Click on the image to visit the site.

October 30, 2007October 31, 2007

Great Skull Anatomy Site

I stumbled across this wonderful anatomy site that focuses on the skull. You can move your mouse over different parts of the skull to highlight their names. You can also mouse over a structure and have the area of the skull highlighted. This is a wonderful study guide if you have to know the parts of the skull.

clipped from www.tk-online.de

October 8, 2007

Cool Image of Ventricles in the Brain

For my research, I’ve been spending time processing brain MRIs and measuring the volume of the brain and lateral ventricles. Here is an image of one of the brains (visualization by FSLView 3.0, with ventricles measured by ITK-Snap). The image is slightly messy because the brain did not extract perfectly (separating brain from non-brain). Also, portions of the ventricles are missing (especially the occipital and temporal horns) due to imperfect MRI resolution and processing. The ventricles are viewed through a cut-away of the 3D-rendered brain.

Note: You MAY NOT use this image without express written consent from me.

September 21, 2007

Diffusion Tensor Imaging and High Angular Resolution Diffusion Imaging

I attended an interesting lecture this week. The professor who spoke talked about Diffusion Tensor Imaging (DTI) as well as about a newer technology they are trying to help develop – High Angular Resolution Diffusion Imaging (HARDI). DTI is based on tensor mathematics and physics. The tensor in DTI is basically a 3×3 matrix (x, y, and z planes) of numbers that represent the diffusion per voxel in the brain. A voxel is a volumetric pixel – a 3D portion of the brain in MR imaging. The highest resolution we can typically get with clinical MR scanners is a cubic mm voxel. So with DTI we have a tensor, a matrix, that describes the diffusion of water molecules within each voxel in the brain. Diffusion in a jar of water or in the ventricles of the brain tends to be fast and spherical. It is less spherical in the gray matter and even less so in the white matter. In fact, the diffusion of water is highly directional in white matter (the myelinated axons of neurons). This means that the water molecules tend to diffuse somewhat parallel to the length of the axon. The movements of these water molecules are picked up by the MR scanner (which is technically “focusing” on the hydrogen atoms in water).
The diffusion per voxel can be quantified by measures of fractional anisotropy (how directional is the movement), Mean Diffusivity (total diffusion within the voxel), and by the eigenvalues of the matrix (basically how far the molecules moved in the direction of the eigenvector).
Back to HARDI. HARDI improves upon DTI by allowing for more directions of the white matter fibers to be separated out than is possible with DTI. There are some areas of the brain where there are a lot of crossing fibers and these areas show up as dark spots on DTI (which looks like a hole in the brain). With HARDI, you can see that the fibers are just more complex than is possible to calculate with DTI.
Both of these methods are useful for measuring the overall integrity (and potentially connectivity) of the white matter in the brain.

August 6, 2007February 26, 2008

The 3D brain

Technology Review has an interesting article about “new” 3D brain imaging software being developed at Thomas Jefferson University Hospital in Philadelphia, PA (I put “new” in quotation marks because there are other similar programs out there; they might not be as polished but some are even open source). Their software fuses MRI, fMRI, and DTI together to create a fairly comprehensive view of the brain: “The fusion of these different images produces a 3-D display that surgeons can manipulate: they can navigate through the images at different orientations, virtually slice the brain in different sections, and zoom in on specific sections.”

The software looks like it is aimed more at neurosurgeons than researchers (i.e., it probably isn’t free like a lot of MRI image processing software). It does produce amazing images (view the images here) and looks like it could be a very useful tool for at least a qualitative approach to brain imaging.

DTI fibers near a tumor

The software is focused a lot on DTI (diffusion tensor imaging) and how the white matter fibers in the brain interact with lesions or tumors. I think that one researcher’s word of caution is important:

“Bruce Fischl, an assistant in neuroscience at Massachusetts General Hospital, says that the idea is ‘interesting’ but cautions that there are a number of levels of ambiguity when talking about connectivity in imaging. ‘Just because you live next to the Mass Pike doesn’t mean that there is an exit,’ he says.”

In other words, don’t get too caught up in the fact that fibers are right by a tumor, they may not really have anything to do with the part of the brain the tumor is most affecting.

In any case, I think that the idea behind this software is amazing. The graphics renderings are impressive (but they are just the pretty pictures – the rendering details may be beneficial in clinical surgery settings but they are not particularly useful in research situations, other than producing nice pictures to go in your publication). This software is very similar to something that I envisioned using a few years ago and I’m glad to see it being developed.

Image credit: Song Lai, Thomas Jefferson University Hospital (borrowed via technologyreview.com)

June 20, 2007June 20, 2007

Dynamically filtering the brain

Researchers believe that the prefrontal cortex acts as a dynamic filter for the brain. Dynamic filtering is selecting needed information for a current task from all the information streaming through the frontal cortex. This is why the prefrontal cortex acts as a dynamic filter, it must sort through the information and pick only that which is currently relevant.

Thompson-Schill et al. (1997) wanted to study the dynamic filtering hypothesis so they had subjects generate verbs associated with presented nouns. In other words, if the person saw a “cat” they might say “meow” or “nap” or something else. Thompson-Schill et al. assigned subjects to a high or low noun-verb selection condition. In the high condition, subjects were shown nouns with many associated verbs (e.g., a ball is shown and subject could produce “bounce,” “hit,” “kick,” or “throw”) whereas in the low condition subjects are shown a noun with only one (in most cases) related verb (e.g., a chair is shown and subject says “sit”).

They conducted this experiment to see if the inferior frontal cortex is associated with just semantic memory (basically long-term-memory-type information) or if it an area that supports working memory processes (retrieving information from semantic memory and working with it—in this case filtering through it for relevant associations). The experimenters found that the inferior frontal cortex (IFC) was more activated in the high-selection conditions than in the low-selection condition. If it had not been more activated then it would merely have been a semantic, long term, memory-related area. Because of the higher activation it was concluded that the IFC was associated with working memory, specifically pulling relevant information from semantic memory. It acts as a filtering mechanism, a dynamic filter.

To confirm this finding Thompson-Schill et al. (1998) conducted another study with brain-damaged patients. They selected subjects with lesions of the IFC. They found that in the high-selection condition these patients failed to produce any verbs 15% of the time. But in the low-selection condition these lesioned subjects performed the same as control subjects. The researchers concluded that because those with IFC lesions could not generate verbs to go along with displayed nouns when there were possibly many to choose between, the lesion caused a deficit in selection. It was not a semantic deficit, but a working memory one. They could not decide what verb to use and so they said nothing. This provided neuropsychological evidence for the IFC acting as a dynamic filter for the frontal cortex, at least as far as semantic information is concerned.

Thompson-Schill et al. (1999) also conducted another study where they looked at the temporal lobe in addition to the IFC. They replicated their previous experiment with one key difference. They had the subjects complete two generative trials (one of naming an action verb like in previous experiments and the other was naming an associated color) with the same list of nouns shown the second time for the subjects. Some repeated the first association task and others did the color one the second time. They found that IFC activation increased when the association task changed but temporal lobe activation decreased the second trial for both association conditions. Gazzaniga, Ivry, and Mangun (2002) sum it up best, “The fact that the decrease was observed is consistent with the idea that semantic attributes, be they relevant or irrelevant to the task at hand, were automatically activated upon presentation of the nouns” (p. 522). This is further evidence that the IFC acts as a dynamic filter for the frontal lobes.

[Note: Contact me if you would like the references cited in my post].

June 15, 2007June 15, 2007

The charitable accumbens

CNN posted an interesting article about how when people choose to be charitable (i.e., give money away) that the nucleus accumbens, which is termed the “pleasure center” of the brain, and the caudate nucleus showed heightened activity. It’s turning out that the nucleus accumbens is involved in far more activities than we’ve ever realized. It’s an area of the brain that is heavily tied to the dopaminergic system and is directly tied to drug use, eating, sex, and pretty much anything else that people can enjoy. In addition, assumed dysfunction or dysregulation of the nucleus accumbens is tied to addictive behaviors. It’s not surprising then that a behavior that is enjoyable to so many – being charitable – is related to activity in the nucleus accumbens. Maybe some people are just Scrooges because they have too little dopamine in their brains [pure speculation and meant to be slightly humorous but it is a hypothesis that could be worth testing].

Image courtesy of benevolink

June 9, 2007June 12, 2007

War-related traumatic brain injuries

An article in the most recent Monitor on Psychology (published by the American Psychological Association) [here’s a link to the article that is accessible for free online: Link) reminded me of something one of my professors in graduate school told our class a couple years ago. He is a clinical neuropsychologist who occasionally does some consulting for the military. After he returned from a consultation with the military he told us that between the war in Afghanistan and the Iraq war there had been 18,000 central nervous system (brain and spinal cord) injuries of soldiers and contract employees serving in those two countries. The majority of the injuries were minor and many were not combat related but there are still thousands of people with moderate to severe CNS injuries that were acquired in war zones. Quoting from the Monitor article:

“Psychologists, particularly neuropsychologists, are stepping in to assess the damage, help patients learn new strategies to compensate while their brains recover, and raise public awareness of the increasing number of servicemen and women with TBIs. In fact, 1,977 service members were treated for them at Defense and Veterans Brain Injury Center (DVBIC) sites from January 2003 to February 2007.”

One reason for high rates of traumatic brain injury in the Iraq (and Afghanistan) war(s) is the improved (compared to previous wars) body armor and other life-saving devices. The downside to fewer fatalities is that there are higher rates of people with severe injuries who survive. The mild TBI rates are shown to be: “between 10 and 20 percent [in some surveys] of soldiers returning from deployments” (Source). It’s great to have fewer fatalities but TBIs can have profound effects on people. Clinical neuropsychologists can help people with TBIs learn how to best cope with their injuries as well as understand how their lives might be different and what they can do to compensate for any difficulties. Most people with mild to moderate TBIs seem to have complete or nearly complete recoveries; however, those with moderate to severe TBIs may have deficits, many very severe, that last the rest of their lives.

There can be myriad short-term problems associated with TBIs (e.g., mental slowing, memory problems, personality changes, concentration and attentional difficulties, etc.) but there are also long-term ones. Research has shown that a person with a history of multiple TBIs is more likely to get Alzheimer’s Disease in old age (well, the research actually shows that there is an over-representation of people with multiple TBIs in the Alzheimer’s population). There is a great need for clinical neuropsychologists currently and in the future to work with and help all of our war veterans who have acquired brain injuries.

June 4, 2007June 4, 2007

Brain Injury Video

Here’s a decent video about brain injury that does a good job of showing how brain injury affects people.

Unfortunately, we don’t have the ability to completely reverse the effects of acquired brain injury. Therapy and rehabilitation can help but if the injuries are severe, completely normal functioning is unlikely ever to return. Prevention is the best medicine in this case; it is unfortunate that prevention is not always possible.The parts of the brain that are most often affected with brain injury are those that have to do with memory.

Another common outcome of brain injury is cognitive slowing – people just don’t seem to think or move or act as quickly after brain injury as they did before. This slowing is due in part to the diffuse axonal injury that occurs (the connections between brain cells {neurons} are broken or twisted as the brain compresses and stretches) with traumatic brain injuries. Even non traumatic brain injuries (e.g., carbon monoxide poisoning) can result in overall cognitive slowing (this slowing often greatly improves over time with mild to moderate brain injuries).It is also fairly common to see personality changes in someone with a recent brain injury – this is mainly due to damage to the frontal lobes. These changes in personality can be the source of great frustration and concern for family, friends, and everyone around the injured person. Dealing with a severe brain injury requires a lot of loving, patience, and care.