Decoding the Mind

Author's note

I am a UC Davis student majoring in Neurobiology, Physiology, and Behavior, and have been an editor for this journal for three years now. I am passionate about neuroscience and psychology. Most particularly, studying the cognitive and physiological aspects of how memory develops. I wrote this article to highlight the neural mechanisms behind working memory and learn more about the specific neural activity that shapes how we encode and retrieve memory. 

Introduction

Have you ever tried memorizing a person’s name or a password? In both of these instances, you are using something called the working memory. In contrast to other forms of memory, such as sensory and long-term memory, working memory retains a small amount of information in a readily accessible form (Cowan et al., 2008). This cognitive function plays a significant role in planning, comprehension, reasoning, and problem-solving (Cowan, 2014). Moreover, it plays a crucial role in higher-order cognitive processes such as decision-making, problem-solving, and learning (Ranganath et al., 2004a). To gain a comprehensive understanding of how working memory functions, researchers have focused on understanding the neural processes and regions involved in its encoding and maintenance.

In this context, Ranganath and colleagues' (2004b) paper titled "Category-Specific Modulation of Inferior Temporal Activity during Working Memory Encoding and Maintenance" stands out as a noteworthy addition to the field of biopsychology. The paper presents a significant contribution to the field by exploring the category-specific modulation of inferior temporal activity during these crucial stages of working memory. In other words, this study examined whether the regions of the brain involved in retrieving different types of information are separate from each other and whether this differentiation occurs before or after the retrieval process. This research provides valuable insight into how different kinds of information, such as faces, objects, and scenes, are represented and maintained in the brain during working memory tasks. 
 

Methods

The researchers employed functional magnetic resonance imaging (fMRI) to investigate the neural underpinnings of category-specific memory retrieval. This type of imaging uses the brain's deoxyhemoglobin concentration to monitor task-induced or spontaneous modulation of neural metabolism (Glover, 2011).

This experiment had two parts to it. In the first phase, participants were shown images of objects, faces, and words and were then asked to memorize them. During the second phase, participants were presented with a series of cues and were asked to recall the image associated with each one. These cues were designed to elicit retrieval of one of the object, face, or word information.

The authors used a block design, where each block consisted of trials from a single category. Block design is a tool used in statistics where cohorts of experimental subjects are placed into groups called blocks. This was done to prevent confounding variables (a factor not being studied that can influence the results) in the within-group study, where all participants were treated with every independent variable. The order of the blocks was systematically varied across participants. Additionally, the authors included a rest condition between each block to allow for baseline activity measurements.

Throughout both the memorization and test phases, fMRI data were collected, allowing researchers to monitor the neural mechanisms of the retrieval. The data analysis focused on identifying brain regions that showed differential activity during the retrieval of the information.

Results and Conclusions

The fMRI results revealed distinct neural activation patterns in the inferior temporal cortex depending on the type of stimuli being encoded and maintained in working memory, as hypothesized. Specifically, when participants were engaged in encoding and maintaining face stimuli, the inferior temporal cortex showed significantly higher activity in the fusiform face area. Moreover, when participants were involved in encoding and maintaining scene stimuli, the inferior temporal cortex displayed increased activity in the parahippocampal place area compared to face and object stimuli. Conversely, during object-related working memory tasks, a different region of the inferior temporal cortex exhibited elevated activation relative to the other stimuli.

These findings suggest that the inferior temporal cortex exhibits category-specific modulation during different stages of working memory. This means that the category of stimuli determines what region of the inferior temporal cortex gets activated and how that leads to memory formation. The results highlight the specialization of this brain region in processing and representing different types of information, such as faces, objects, and scenes, during working memory tasks.

Furthermore, this study examined the relationship between individual differences in working memory capacity and the category-specific modulation of inferior temporal activity. Interestingly, participants with higher working memory capacity demonstrated enhanced activation in the inferior temporal cortex across all stimulus categories. This indicates a more efficient engagement of this region during working memory tasks.

References

Cowan, N. (2014). Working memory underpins cognitive development, learning, and education. Educational psychology review, 26(2), 197–223. https://doi.org/10.1007/s10648-013-9246-y 

Cowan, N. (2008). What are the differences between long-term, short-term, and working memory? Progress in brain research, 169, 323–338.
https://doi.org/10.1016/S0079-6123(07)00020-9

Glover, G. H. (2011). Overview of functional magnetic resonance imaging. Neurosurgery Clinics of North America, 22(2),:133–vii.
https://doi.org/10.1016/j.nec.2010.11.001

Ranganath, C., Cohen, M. X., Dam, C., & D'Esposito, M. (2004). Inferior temporal, prefrontal, and hippocampal contributions to visual working memory maintenance and associative memory retrieval. The Journal of Neuroscience, 24(16), 3917–3925. https://doi.org/10.1523/JNEUROSCI.5053-03.2004

Ranganath, C., DeGutis, J., & D’Esposito, M. (2004). Category-specific modulation of inferior temporal activity during working memory encoding and maintenance. Cognitive Brain Research, 20(1), 37–45.
https://doi.org/10.1016/j.cogbrainres.2003.11.017