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Paper   IPM / Cognitive Sciences / 14532
School of Cognitive Sciences
  Title:   Maintenance of spatial information modulates beta rhythms within MT cortex
1.  Z. Bahmani Dehkordi
2.  M. Daliri
3.  Y. Merrikhi
4.  M. Parsa
5.  B. Noudoost
  Status:   In Proceedings
  Proceeding: 2016­-S-­8148-­SfN
  Year:  2016
  Supported by:  IPM
Psychophysical experiments have shown that remembering a location enhances visual discrimination performance at that location. Findings in our lab indicate that neurons in extrastriate visual areas receive a strong top­down signal from prefrontal cortex during the maintenance of spatial information. Although delay­period activity is very weak or non­existent in these visual areas, their sensitivity to incoming visual signals is enhanced during spatial memory maintenance. One possible explanation for this increase in sensitivity to visual input without an increase in baseline firing rate is that the top­down signal provides a sub­threshold modulation. Since the local field potentials (LFPs) are believed to reflect the level of input to an area, we sought to determine whether, and in what frequencies, extrastriate LFPs are modulated during spatial memory maintenance. For this purpose, we recorded neuronal spiking and LFP signals in the middle temporal (MT) area of rhesus monkeys performing a memory­guided saccade task. In this task, the target was presented for one second; the monkey had to remember the target location during a 1.5­2 second blank delay, and then saccade to the remembered location when the fixation point disappeared. Linear array electrodes were used to simultaneously record the activity of multiple MT neurons and LFPs. We measured the power density function (PSD) of the LFPs at each recording site prior to target presentation, during target presentation, and during the memory period. The PSDs were normalized based on the PSD prior to target presentation.The beta (15­30 Hz) power significantly increased during the memory period. Evaluating the temporal relationship between spikes and LFP signals revealed a significant increase in the locking between spikes and the phase of ongoing beta oscillations during the memory period. We also found that the beta power during the memory period predicted the upcoming saccade accuracy and the reaction time: trials with higher beta power had more precise and faster saccadic responses. These findings provide a mechanistic insight into how the maintenance of spatial information contributes to enhanced sensory processing, potentially underlying the behavioral effects of spatial working memory.

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