Memory in the Brain research

Memory in the Brain

Daisy Tseng

Mt. San Antonio College

Biological Psychology

Online

Dr. John Pellitteri

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Memory in the Brain

According to recent studies examining memories of highly arousing real-life events, such

as the 9/11 terrorist attacks, memories of emotional events differ from everyday events in their

ratings of vividness, recollection, and belief in accuracy (Sharot et al., 2004). This composes a

“subjective sense of remembering” because the objective accuracy of these memories are the

same regardless of emotion. To further examine this occurrence, Sharot, Delgado, and Phelps

(2004) conducted a study that utilized event-related functional magnetic resonance imaging

(fMRI) to explore blood oxygen level dependent (BOLD) signal changes associated with the

subjective feeling of remembering emotional and neutral photos.

For this study, Sharot et al. (2004) utilized a controlled laboratory paradigm known as the

‘remember’/’know’ procedure. The dual process theory of recognition states that ‘remember’ and

‘know’ responses are two different memory processes. Thus, the participants in this study had to

assign previously-experienced stimuli as either ‘remembered’ or ‘known.’ Remembered stimuli

is based on recollection, or recognition supplemented with associative information, whereas

known stimuli is based on familiarity, or memory without contextual information (Sharot et al.,

2004).

There were a total of 13 healthy right-handed subjects (5 male and 8 female) included in

this study’s analysis. Sharot et al. (2004) selected 75 negatively arousing photos and 75 neutral

photos from the International Affective Photo Series (IAPS) to be used as the stimuli presented

to the participants. They classified these two categories by examining each photo’s standard

scores for emotional arousal and emotional valence.

The participants first completed an incidental encoding task consisting of 120 trials. Each

trial included the showing of either an emotional or neutral image for two seconds, presentation

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of a rating task judging the visual complexity of the photo for two seconds, and lastly fixation for

ten seconds (Sharot et al., 2004). An hour later, the fMRI scanning session began with a

structural scan and then six functional scans. Each of the functional scans consisted of 25 trials,

which included viewing the photo for two seconds, making recognition judgments for two

seconds by indicating ‘remember’ or ‘know’ after the photo disappears, and looking at the

fixation cross for ten seconds (Sharot et al., 2004).

After analyzing the patterns of BOLD activation, Sharot et al. (2004) concluded that

depending on the level of emotionality of a stimuli, distinct subregions of the medial temporal

lobe have different influences on recognition judgments. The researchers found that in regards to

emotional material, the heightened feeling of remembering is associated with increased activity

in the amygdala (Sharot et al., 2004). When making a ‘remember’ judgment for an emotional

photo, an individual depends on the feeling of arousal signals and intensified perceptual fluency

associated with the amygdala. This enhances the subjective experience of retrieval without

necessarily increasing accuracy (Sharot et al., 2004). Meanwhile, when a participant makes a

‘remember’ judgment for neutral photos, they rely on recognizing visual details, which

corresponds to increased activity in the parahippocampal cortex (Sharot et al., 2004).

While Sharot et al. (2004) utilized a typical artificial laboratory stimulation, Frings,

Mader, and Hüll (2010) conducted a study assessing memory-related fMRI activation with the

natural and ecologically valid stimulation of watching television news. By developing a

paradigm that closely mimics everyday life situations of information encoding and acquisition,

the researchers aimed to test brain activation during more complex, real-life stimulation (Frings

et al., 2010). Furthermore, the researchers believed that the natural, real-life paradigm would

create a more comfortable environment which would decrease possible anxiety effects on the test

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performance (Frings et al., 2010).

The participants in this study were 17 neurologically healthy subjects (9 females and 8

males) ranging from 22 years to 70 years old. The natural stimuli chosen for the memory task

were six clips from a German daily TV news show called ‘Tagesschau.’ Each clip contained a

complete news story in 20-30 seconds. For the control condition, Frings et al. (2010) took the

same six news clips but reversed its audio and randomly rearranged its visual pixels. Thus, its

sound and visual presentation were no longer distinguishable nor meaningful. Additionally, the

researchers randomly distributed a fixation cross baseline condition.

Before the memory task and MR scanning was conducted, the subjects were asked to

listen and watch carefully as they would be asked to recall the six news clips in as much detail as

possible. During the memory paradigm, “208 BOLD-sensitive echo planar images of the entire

cerebrum were acquired using a 3 Tesla Siemens TIM-Trio” (Frings et al., 2010, p. 2).

Afterward, the researchers contrasted brain activity (regional BOLD response) during the

episodic memory task that required semantic processing to the control condition that did not need

semantic or episodic memory processing (Frings et al., 2010).

After conducting a one-sample T-test analysis for this main memory task effect, Frings et

al. (2010) found a left-lateralized activation pattern that primarily involved the lateral temporal

cortex, frontal cortex, and left hippocampus. The researchers believe that this observed activation

correlates to the ventral stream brain regions that have been previously studied to be crucial in

language processing. For instance, the areas include the left temporal pole, which is known as the

semantic hub, as well as the inferior, posterior temporal activated region that is termed the basal

temporal language area (Frings et al., 2010). Therefore, Frings et al. (2010) conclude that the

majority of the observed areas of activation pertain to semantic processing of incoming

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information, which is necessary for the hippocampus to encode episodic memory.

The secondary purpose of this study was to examine how age differences would affect

brain activation during information acquisition. Frings et al. (2010) performed a multiple

regression analysis to study the fMRI age effect. The analysis organized in table two of the

research article revealed a significant relation between older age and greater activation in the

superior temporal regions of the left hemisphere (Frings et al., 2010). The researchers

hypothesize that this increased activity in the left superior temporal regions for the elderly was

due to how the elderly subjects needed to increase their efforts and their attention to memory in

order to perform as well as the younger participants (Frings et al., 2010).

Frings et al. (2010) noted that another possible explanation for this observed age effect on

activation is the altered hemodynamics in elderly subjects that are not related to cognition. In

comparison to the main task effect previously detailed, the researchers claim that the age-effect

observations and analyses were considered a “secondary, preliminary result of the current study

that requires replication by studies assessing larger numbers of participants” (Frings et al., 2010,

p. 6). Thus, there is no formal, concrete conclusion for the age-effect aspect of this study as the

researchers need to conduct further studies to solidify the validity of their claims.

Due to the less controlled nature of this study that mimicked complex real-life

stimulation, there were many factors involved in the memory task. A study that focused

specifically on verbal episodic memory was conducted by Nyberg, Mclntosh, Houle, Nilsson,

and Tulving (1996). They utilized positron emission tomography (PET) to explore cerebral blood

flow associated with verbal episodic retrieval.

In the study, each of the 11 right-handed young volunteers went through an experimental

procedure consisting of “four conditions in which regional cerebral blood flow (rCBF) was

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estimated from PET counts” (Nyberg et al., 1996, p. 715). The participants were auditorily

presented with two lists of 80 words. Half of the words were read by a male voice, while the

other half were read by a female voice. As stated in the article, the first condition was the visual

recognition of words following meaning-based encoding. The meaning-based encoding task

consisted of the participant deciding whether the words they heard referred to living or

non-living things. The second condition was the visual recognition of words following

perceptual encoding. In the perceptual encoding task, subjects had to decide whether the words

were read out loud by a male or female. The third and fourth conditions were visual recognition

of non-studied words and a baseline word-reading condition, respectively (Nyberg et al., 1996).

During each of the eight recognition tests for each participant, PET scans were obtained

with a GEMS-Scanditronix PC 2048-15B head scanner (Nyberg et al., 1996). Afterward, Nyberg

et al. (1996) cross-correlated the rCBF pattern during recognition performance following

meaning-based encoding with the proportion of correctly recognized items. After the correlations

were computed, they discovered a significant positive correlation between recognition

performance and brain activity in the left anterior medial temporal lobe (Nyberg et al., 1996).

Likewise, Nyberg et al. (1996) found a positive correlation between recognition performance

following perceptual encoding and activity in this same region. This further demonstrates the

reliability of this correlation in the sample.

These correlational analyses outcomes suggested a possible connection between verbal

episodic retrieval and left medial temporal lobe activity (Nyberg et al., 1996). Thus, the

researchers hypothesized that “recognition following meaning-based encoding, which resulted in

the highest memory performance, should be associated with higher activity in the left medial

temporal lobe” (Nyberg et al., 1996, p. 716).

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To test this expectation, Nyberg et al. (1996) conducted a partial least squares analysis.

The analysis indicated a spatial pattern in brain areas that differentiated recognition following

meaning-based encoding from the other three conditions studied. The components with the

strongest positive weight were found to be located in the left and right medial temporal lobe

(Nyberg et al., 1996). The researchers therefore concluded that activity in the medial temporal

lobe is indeed associated with verbal and not only visual retrieval. Furthermore, the partial least

squares analysis also confirmed their hypothesis that an increase in left medial temporal activity

correlates with increased retrieval.

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References

Frings, L., Mader, I., & Hüll, M. (2010). Watching TV news as a memory task–brain activation

and age effects. BMC Neuroscience, 11(1), 106–106.

https://doi.org/10.1186/1471-2202-11-106

Nyberg, L., Mclntosh, A., Houle, S., Nilsson, L., & Tulving, E. (1996). Activation of medial

temporal structures during episodic memory retrieval. Nature (London), 380(6576),

715–717. https://doi.org/10.1038/380715a0

Sharot, T., Delgado, M., & Phelps, E. (2004). How emotion enhances the feeling of

remembering. Nature Neuroscience, 7(12), 1376–1380. https://doi.org/10.1038/nn1353