Cognitive Neuroscience - 2.4 Flashcards
1980s a technique developed called what?
MRI
(Magnetic resonance imaging)
Definition of fMRI
A brain imaging technique that measures how blood flow changes in response to cognitive activity.
Definition of MRI
Brain imaging technique that creates images of structures within the brain. See also Functional magnetic resonance imaging (fMRI).
What did MRI made possible?
create images of structures within the brain, was introduced for clinical practice. Since then, it has become a standard technique for detecting tumours and other brain abnormalities.
Disadvantage of MRI
it doesn’t indicate neural activity.
Another technique fMRI (functional magnetic resonance imaging)
enabled what?
enabled researchers to determine how various types of cognition activate different areas of the brain.
Most of the brain imaging experiments that have provided evidence of…
localization of function has involved determining which brain areas were activated when people observed pictures of different objects.
fMRI takes advantage of the fact that
how does fMRI work
- blood flow increases in areas of the brain activated by a cognitive task.
- The measurement of blood flow is based on the fact that haemoglobin, which carries oxygen in the blood, contains a ferrous (iron) molecule and therefore has magnetic properties.
- If a magnetic field is presented to the brain, the haemoglobin molecules line up like tiny magnets.
- fMRI indicates the presence of brain activity because the haemoglobin molecules lose some of the oxygen they are transporting in areas of high brain activity.
Summary of how fMRI works
- This makes the haemoglobin more magnetic, so these molecules respond more strongly to the magnetic field. Thus, the fMRI apparatus determines the relative activity of various areas of the brain by detecting changes in the magnetic response of the haemoglobin. The measured changes are blood-oxygen-level-dependent and the fMRI signal is therefore referred to as the BOLD signal.
How fMRI works refers to a haemodynamic response and not neuronal responses
that these two types of responses are linked to each other in a complex way (Arthurs & Boniface, 2002). This means that fMRI does not directly measure neural activity.
What does this figure show?
- With the person’s head in the scanner. As a person engages in a cognitive task such as perceiving an image, the BOLD signal is determined for thousands of voxels, which are small cube-shaped areas of the brain about two or three mm on a side. One way to think about voxels is that they are like the small square pixels that make up digital photographs or the image on your computer screen, but since the brain is three-dimensional, voxels are small cubes rather than small squares.
- Figure 2.14b shows the result of an fMRI scan, but only one single slice of it! Increases or decreases in brain activity associated with cognitive activity are indicated by colours, with specific colours indicating the amount of activation.
What are voxels
Small cube-shaped areas in the brain used in the analysis of data from brain scanning experiments.
Looking at pictures of faces has been found to activate a specific area of the brain called
fussiform face area (FFA)
This area has been given this name because it is located in the fusiform gyrus on the underside of the temporal lobe
What is FFA/Fusiform face area is?
An area in the temporal lobe that contains many neurons that respond selectively to faces.
More evidence for localisation of function coming from fMRI experiments showing that perceiving pictures represented indoor and outdoor scenes activates what/.
PPA
Parahippocampal place area
(EBA) extrastriate body area is activated by pictures of what?
pictures of bodies and parts of bodies (but not by faces)
Huth Nishimoto Vo and Galland (2012) conducted an fMRI experiment using stimuli similar to what we see in the environment by having participants view film clips
PROCEDURE
Participants in this study viewed two hours of film clips while in a brain scanner. To analyze how the voxels in these participants’ brains responded to different objects and actions in the films, Huth and colleagues created a list of 1705 different objects and action categories and determined which categories were present in each film scene.
Figure 2.17 shows four scenes and the categories (labels) associated with them. By determining how each voxel responded to each scene and then analyzing his results using a complex statistical procedure, Huth was able to determine what kinds of stimuli each voxel responded to. For example, one voxel responded well when streets, buildings, roads, interiors and vehicles were present.
What does this figure show about Huth et al
- types of stimuli that cause voxels across the surface of the brain to respond.
- present an interesting paradox. On one hand, the results confirm the earlier research that identified specific areas of the brain responsible for the perception of specific types of stimuli like faces, places and bodies. On the other hand, these new results reveal a map that stretches over a large area of the cortex. As we will now see, even though there is a great deal of evidence for localization of function, we need to consider the brain as a whole in order to understand the physiological basis of cognition.
What does this figure show about why objects and actions similar to each other are located in each other in the brain?
- The reason there are two areas for humans and two for animals is that each area represents different features related to humans or animals. For example, the area labelled “human” at the bottom of the brain (which is actually on the underside of the brain) corresponds to the fusiform face area (Figure 2.15b), which responds to all aspects of faces.
- The human area higher on the brain responds specifically to facial expressions, important for emotion recognition. The areas labelled “talking” correspond to Broca’s and Wernicke’s areas, which as we have seen before, also play an important function in language.
While a number of areas of the brain participate in perception of a face, other areas also respond to various reactions to a face. For example
- see someone walking down the street, looking at the person’s face activates many neurons in your FFA, plus neurons in other areas that are responding to the face’s form. Your response to that person’s face however, may go beyond simply “That’s a person’s face.” You may also be affected by whether the person is looking at you, by how attractive you think the person is, by any emotions the face may elicit, and by your reactions to the person’s facial expression. As it turns out, different areas in the brain are activated by each of these responses to a face (see Figure 2.19). Looking at a face thus activates a number of areas involved in perceiving the face, plus other areas associated with reactions elicited by the face.
Figure 20 shows what: shows
What is remarkable about the rolling red ball is that even though it causes activity in a number of separated areas in the brain, our experience contains little or no evidence of this widely distributed activity. We just see the ball! The importance of this observation extends beyond perceiving a rolling red ball to other cognitive functions, such as memory, language, making decisions and solving problems, all of which involve distributed activity in the brain.
For example, research on the physiology of memory, which we will consider in detail in Chapters 5 and 7, has revealed that multiple areas in every lobe of the brain are involved in storing memories for facts and events and then remembering them later. Recalling a fact or remembering an event not only elicits associations with other facts or events but can also elicit visual, auditory, smell or taste perceptions associated with the memory; emotions elicited by the memory; and other thought processes as well. Additionally, there are different types of memory—short-term memory, long-term memory, memories about events in a person’s life, memories for facts, and so on—all of which activate different, although sometimes partially overlapping, areas of the brain.
