Neurophysiological Study: Neurophysiological Research on Orientation Discrimination in a Working Memory Task

Background

Recognizing and remembering the spatial orientation of the environment is a crucial component of visuospatial behavior. Accurately storing and recalling this information helps us navigate in space and respond adaptively to rapid changes. However, despite extensive research on orientation memory in the literature, these studies predominantly focus on the early visual areas using functional magnetic resonance imaging (fMRI) to maintain precise descriptions of stimuli. Simultaneously, there is sporadic information on the involvement of individual subregions in the frontal cortex. Yet, there is a lack of systematic research at the stage of comparing current environmental changes and orientation information in memory. Understanding the mechanisms of this operation is vital not only for grasping how the visual system quickly recognizes fundamental features of the visual environment but also for revealing the brain’s reference system that maintains the stability of these memories.

Research Source

The research paper, titled “Neurophysiological Study of Orientation Discrimination in a Working Memory Task,” was authored by E.S. Mikhaylova and N.Yu. Gerasimenko, both from the Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Sciences. This paper was published in the 2023 issue of the journal “Human Physiology” (vol. 49, suppl. 1, pp. S1–S12).

Research Methods

Subjects

The experiment involved 33 participants (16 males and 17 females) with an average age of 22.57 ± 0.46 years. All participants had normal vision, signed informed consent, and adhered to the approval of the ethics committee of the institute.

Stimuli

The experiment used high-contrast black and white sinusoidal gratings, with tilt angles of 0° (horizontal), 90° (vertical), and 45°. Each stimulus had a size of 5.5 degrees. To simulate scenarios that compare new information with information stored in short-term memory, pairs of gratings with different orientations were presented to participants in random order. The paired gratings consisted of three identical orientations (0°–0°, 90°–90°, and 45°–45°) and six different orientations (0°–90°, 0°–45°, 90°–0°, 90°–45°, 45°–0°, and 45°–90°).

Experimental Procedure

During the experiment, participants sat in a dark, sound-attenuated room on a comfortable chair, 120 cm away from the display. Stimuli were presented on the screen using E-Prime 2.0 software. Each sequence consisted of the following events: a 100 ms green dot signal, a black fixation point (random duration between 1500–1700 ms), a 100 ms reference stimulus, followed by a 1500–1800 ms interval (with fixation point), a 100 ms test stimulus, and a 3000 ms interval (fixation point). Each pair of reference and test stimuli was presented 30 times, making a total of 270 stimulus pairs, with the experiment lasting approximately 30 minutes. A break of 5–7 minutes was given mid-experiment.

Participants were instructed to judge whether the orientations of the reference and test stimuli were the same and to press the corresponding key, with accuracy and response delay recorded.

EP (Evoked Potential) Registration and Analysis

EEG was recorded using a 128-channel system from Geodesics, with the HydroCel Geodesic Sensor Net cap. EEG data were processed using Netstation software version 4.5.4, with signals filtered (0.5–45 Hz) and segmented into 1300 ms epochs, including a 300 ms baseline during the test stimulus. Segments containing ocular movements and muscle artifacts were removed, and the average evoked potentials (EP) for each participant were calculated.

The analysis focused on the caudal cortical regions’ P100 and N150 components in the EEG, which are early components related to sensory signal processing.

Analysis

The variations of evoked potential components in different brain regions (occipital, parietal, temporal) and changes in the N240 component in the frontal region were analyzed using multifactor ANOVA. Repeated measures ANOVA (RM ANOVA) was employed to statistically analyze the amplitudes of evoked potential components in matching (i.e., reference and test stimuli matching) and non-matching cases, using Greenhouse–Geisser correction and Newman-Keuls correction for multiple comparisons.

Results

Psychological Measurement Indicators

Response Time (RT) and accuracy indicated that RT significantly increased, and accuracy slightly improved when the test and reference orientations did not match, consistent with other literature. Specifically, the RT was larger in non-matching conditions than in matching conditions, especially when the test orientation was vertical (p < 0.001).

P100 and N150 Component Analysis

In sensory signal processing, the EP component P100 in the occipital region significantly increased irrespective of matching or non-matching conditions. Additionally, P100 also significantly increased in the parietal and temporal regions, indicating that higher levels of visual processing were involved in the comparison operation.

N240 Performance in the Frontal Cortex

Compared to the matching condition, the negative amplitude of the N240 component in the frontal cortex significantly increased in the non-matching condition (p < 0.0005), indicating that the frontal cortex is highly sensitive to the differences between current signal and memory signal.

Modeling Source Distribution

Using high-density recordings of evoked activities and dipole modeling methods revealed significant differences in dipole current densities in multiple brain regions (frontal, occipital, parietal, and temporal) for matching and non-matching conditions. This indicates that these areas are not only involved in early sensory analysis but also play critical roles in later cognitive processing stages.

Discussion and Conclusion

This study, using EEG recordings, demonstrates that the brain processes and compares current signals with memory signals primarily in the occipital region during early sensory detection, with participation from the parietal and temporal regions. Non-matching information ultimately emerges in the frontal cortex, showing significant differences in later cognitive processing stages. The results highlight the interactions and information transfer mechanisms between different brain regions, emphasizing the importance of fronto-occipital collaboration. These findings provide empirical support for theories of short-term memory mechanisms and suggest important research directions in exploring functional interactions between the frontal and visual regions.

Such research deepens our understanding of visual working memory and its neural mechanisms, aiding in the future improvement of cognitive training methods and the development of novel brain-computer interface technologies.