Posts tagged psychology

The Who asked “who are you?” but Dartmouth neurobiologist Jeffrey Taube asks “where are you?” and “where are you going?” Taube is not asking philosophical or theological questions. Rather, he is investigating nerve cells in the brain that function in establishing one’s location and direction.

Taube, a professor in the Department of Psychological and Brain Sciences, is using microelectrodes to record the activity of cells in a rat’s brain that make possible spatial navigation — how the rat gets from one place to another — from “here” to “there.” But before embarking to go “there,” you must first define “here.”

Survival Value

"Knowing what direction you are facing, where you are, and how to navigate are really fundamental to your survival," says Taube. "For any animal that is preyed upon, you’d better know where your hole in the ground is and how you are going to get there quickly. And you also need to know direction and location to find food resources, water resources, and the like."

Not only is this information fundamental to your survival, but knowing your spatial orientation at a given moment is important in other ways, as well. Taube points out that it is a sense or skill that you tend to take for granted, which you subconsciously keep track of. “It only comes to your attention when something goes wrong, like when you look for your car at the end of the day and you can’t find it in the parking lot,” says Taube.

Perhaps this is a momentary lapse, a minor navigational error, but it might also be the result of brain damage due to trauma or a stroke, or it might even be attributable to the onset of a disease such as Alzheimer’s. Understanding the process of spatial navigation and knowing its relevant areas in the brain may be crucial to dealing with such situations.

The Cells Themselves

One critical component involved in this process is the set of neurons called “head direction cells.” These cells act like a compass based on the direction your head is facing. They are located in the thalamus, a structure that sits on top of the brainstem, near the center of the brain.

He is also studying neurons he calls “place cells.” These cells work to establish your location relative to some landmarks or cues in the environment. The place cells are found in the hippocampus, part of the brain’s temporal lobe. They fire based not on the direction you are facing, but on where you are located.

Studies were conducted using implanted microelectrodes that enabled the monitoring of electrical activity as these different cell types fired.

Taube explains that the two populations — the head direction cells and the place cells — talk to one another. “They put that information together to give you an overall sense of ‘here,’ location wise and direction wise,” he says. “That is the first ingredient for being able to ask the question, ‘How am I going to get to point B if I am at point A?’ It is the starting point on the cognitive map.”

The Latest Research

Taube and Stephane Valerio, his postdoctoral associate for the last four years, have just published a paper in the journal Nature Neuroscience, highlighting the head direction cells. Valerio has since returned to the Université Bordeaux in France.

The studies described in Nature Neuroscience discuss the responses of the spatial navigation system when an animal makes an error and arrives at a destination other than the one targeted — its home refuge, in this case. The authors describe two error-correction processes that may be called into play — resetting and remapping — differentiating them based on the size of error the animal makes when performing the task.

When the animal makes a small error and misses the target by a little, the cells will reset to their original setting, fixing on landmarks it can identify in its landscape. “We concluded that this was an active behavioral correction process, an adjustment in performance,” Taube says. “However, if the animal becomes disoriented and makes a large error in its quest for home, it will construct an entirely new cognitive map with a permanent shift in the directional firing pattern of the head direction cells.” This is the “remapping.”

Taube acknowledges that others have talked about remapping and resetting, but they have always regarded them as if they were the same process. “What we are trying to argue in this paper is that they are really two different, separate brain processes, and we demonstrated it empirically,” he says. “To continue to study spatial navigation, in particular how you correct for errors, you have to distinguish between these two qualitatively different responses.”

Taube says other investigators will use this distinction as a basis for further studies, particularly in understanding how people correct their orientation when making navigational errors.

(Source: sciencedaily.com)

Decreased activity of a group of genes may explain why in young children the “fear center” of the anxious brain can’t learn to distinguish real threats from the imaginary, according to a new University of Wisconsin study.

The study, published this week in the Proceedings of the National Academy of Sciences (PNAS), lays out evidence that young primates with highly anxious temperaments have decreased activity of specific genes within the amygdala, the brain’s fear center.

The authors hypothesize that this may result in over activity of the brain circuit that leads to higher risk for developing disabling anxiety and depression.

This may be particularly important since the genes involved play a major role in forming the brain connections needed for learning about fears. While all children have fears and anxieties, the authors suggest that children with low levels of activity of these genes develop anxious dispositions because they fail to learn to cope by overcoming their early childhood fears.

“Working with my close collaborator and graduate student, Drew Fox, we focused on understanding the function of genes that promote learning and plasticity in the amygdala,” says Dr. Ned H. Kalin, chair of psychiatry at the University of Wisconsin School of Medicine and Public Health, who led the research. “We found reduced activity in key genes that could impair the ability to sculpt the brain, resulting in a failure to develop the capacity to discriminate between real and imaginary fears.”

Kalin says the study helps support the need for early intervention in children identified as excessively shy and anxious. It may also point a way to better treatments aimed at decreasing the likelihood of children developing more severe psychiatric problems. Anxiety in children is quite common and can lead to anxiety and depression in adolescence and often precedes anxiety disorders, depression and substance abuse in adults.

Most small children go through a phase when they’re frightened of many things, including monsters or new social situations, Kalin says, but their maturing brains soon learn to distinguish real threats from the imaginary. But some children do not adapt, generalize their fears to numerous situations, and may later develop serious anxiety and mood disorders. These children tend to be more sensitive to stress, produce more stress hormones and have heightened nervous-system activity.

Kalin, Fox and co-authors wondered whether some differences in the developing amygdala prevent it from learning how to regulate and adapt to anxiety. Kalin’s earlier work identified a subset of young monkeys, similar to extremely shy children, with an inherited anxious disposition. Using brain imaging, the authors showed that high levels of amygdala activity predicted trait-like anxiety in anxious young primates. Like their stable and enduring anxious dispositions, these individuals also had chronically elevated levels of amygdala activity.

“We believe that this pinpoints a critical region in the brain that determines an individual’s level of trait anxiety,’’ Kalin explains.

In examining a specific part of the amygdala, the central nucleus, the researchers analyzed gene expression, which reflects both environmental and inherited influences. Within the central nucleus of the amygdala the authors found that anxious individuals tended to have decreased expression of a gene called neurotrophic tyrosine kinase, receptor, type 3 (NTRK3). Low levels of this gene that encodes for a brain cell surface receptor may be why the amygdala of an anxious monkey or child is chronically overactive and unable to overcome anxiety and fears.

“This is the first demonstration that the early risk to develop anxiety and depression may be related to the underactivity of particular genes in the developing primate amygdala,’’ Kalin says. “These findings have provided the basis for our hypothesis that can explain the early childhood risk to develop anxiety and depression. It also suggests some creative ways to help children with extreme anxiety by developing new treatments focused on increasing the activity of specific genes involved in facilitating the brain development that underlies fear learning and coping.”

(Source: newswise.com)

A study led by researchers at Boston University School of Medicine (BUSM) provides novel insight into the impact that Huntington’s disease has on the brain. The findings, published online in Neurology, pinpoint areas of the brain most affected by the disease and opens the door to examine why some people experience milder forms of the disease than others.

Richard Myers, PhD, professor of neurology at BUSM, is the study’s lead/corresponding author. This study, which is the largest to date of brains specific to Huntington’s disease, is the product of nearly 30 years of collaboration between the lead investigators at BUSM and their colleagues at the McLean Brain Tissue Resource Center, Massachusetts General Hospital and Columbia University.

Huntington’s disease (HD) is an inherited and fatal neurological disorder that typically is diagnosed when a person is approximately 40 years old. The gene responsible for the disease was identified in 1993, but the reason why certain neurons or brain cells die remains unknown.

The investigators examined 664 autopsy brain samples with HD that were donated to the McLean Brain Bank. They evaluated and scored more than 50 areas of the brain for the effects of HD on neurons and other brain cell types. This information was combined with a genetic study to characterize variations in the Huntington gene. They also gathered the clinical neurological information on the patients’ age when HD symptoms presented and how long the patient survived with the disease.

Based on this analysis, the investigators discovered that HD primarily damages the brain in two areas. The striatum, which is located deep within the brain and is involved in motor control and involuntary movement, was the area most severely impacted by HD. The outer cortical regions, which are involved in cognitive function and thought processing, also showed damage from HD, but it was less severe than in the striatum.

The investigators identified extraordinary variation in the extent of cell death in different brain regions. For example, some individuals had extremely severe outer cortical degeneration while others appeared virtually normal. Also, the extent of involvement for these two regions was remarkably unrelated, where some people demonstrated heavy involvement in the striatum but very little involvement in the cortex, and vice versa.

“There are tremendous differences in how people with Huntington’s disease are affected,” Myers said. “Some people with the disease have more difficulty with motor control than with their cognitive function while others suffer more from cognitive disability than motor control issues.”

When studying these differences, the investigators noted that the cell death in the striatum is heavily driven by the effects of variations in the Huntington gene itself, while effects on the cortex were minimally affected by the HD gene and are thus likely to be a consequence of other unidentified causes. Importantly, the study showed that some people with HD experienced remarkably less neuronal cell death than others.

“While there is just one genetic defect that causes Huntington’s disease, the disease affects different parts of the brain in very different ways in different people,” said Myers. “For the first time, we can measure these differences with a very fine level of detail and hopefully identify what is preventing brain cell death in some individuals with HD.”

The investigators have initiated extensive studies into what genes and other factors are associated with the protection of neurons in HD, and they hope these protective factors will point to possible novel treatments.

(Source: bumc.bu.edu)

At ‘rest,’ right hemisphere of the brain ‘talks’ more than the left hemisphere does

People who like to nap say it helps them focus their minds post a little shut eye. Now, a study from Georgetown University Medical Center may have found evidence to support that notion.

The research, presented at Neuroscience 2012, the annual meeting of the Society for Neuroscience, found that when participants in a study rested, the right hemisphere of their brains talked more to itself and to the left hemisphere than the left hemisphere communicated within itself and to the right hemisphere – no matter which of the participants’ hands was dominant. (Neuroscientists say right-handed people use their left hemisphere to a greater degree, and vice versa.)

Results of this study, the first known to look at activity in the two different hemispheres during rest, suggests that the right hemisphere “is doing important things in the resting state that we don’t yet understand,” says Andrei Medvedev, Ph.D., an assistant professor in the Center for Functional and Molecular Imaging at Georgetown. The activities being processed by the right hemisphere, which is known to be involved in creative tasks, could be daydreaming or processing and storing previously acquired information. “The brain could be doing some helpful housecleaning, classifying data, consolidating memories,” Medvedev says. “That could explain the power of napping. But we just don’t know yet the relative roles of both hemispheres in those processes and whether the power nap might benefit righties more then lefties.”

To find out what happens in the resting state, the research team connected 15 study participants to near-infrared spectroscopy (NIRS) equipment. This technology, which is low cost and portable, uses light to measure changes in oxygenated hemoglobin inside the body.

The study participants wore a cap adorned with optical fibers that delivers infrared light to the outermost layers of the brain and then measures the light that bounces back. In this way, the device can “see” which parts of the brain are most active and communicating at a higher level based on increased use of oxygen in the blood and heightened synchronicity of their activities.

"The device can help delineate global networks inside the brain — how the components all work together," Medvedev says. "The better integrated they are, the better cognitive tasks are performed."

To their surprise, the researchers found that left and right hemispheres behaved differently during the resting state. “That was true no matter which hand a participant used. The right hemisphere was more integrated in right-handed participants, and even stronger in the left-handed,” he says.

Medvedev is exploring the findings for an explanation. And he suggests that brain scientists should start focusing more of their attention on the right hemisphere. “Most brain theories emphasize the dominance of the left hemisphere especially in right handed individuals, and that describes the population of participants in these studies,” Medvedev says. “Our study suggests that looking at only the left hemisphere prevents us from a truer understanding of brain function.”

(Source: eurekalert.org)