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DTSTART:20320314T030000 RDATE:20321107T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20330313T030000 RDATE:20331106T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20340312T030000 RDATE:20341105T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20350311T030000 RDATE:20351104T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20360309T030000 RDATE:20361102T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT BEGIN:DAYLIGHT DTSTART:20370308T030000 RDATE:20371101T010000 TZOFFSETFROM:-0500 TZOFFSETTO:-0400 TZNAME:America/New_York EDT END:DAYLIGHT END:VTIMEZONE BEGIN:VEVENT UID:09b82139e1143c68623e293fd7e34546 CATEGORIES:Human and computer vision series:Spring 2015 CREATED:20151203T141544 SUMMARY:Defining a role for prefrontal cortex in memory-guided sensory decision-making LOCATION:University of Rochester\, Departments of Neurobiology & Anatomy\, Brain & Cognitive Science\, Biomedical Engineering\, and C DESCRIPTION:
Comparing two visual stimuli that occur at different times demands the c
oordination of bottom-up and top-down processes. Such tasks require process
ing and storage of sensory stimuli, followed by their retrieval and compari
son leading to perceptual decision. It is widely accepted that the lateral
prefrontal cortex (LPFC) is an area that integrates the various components
of such tasks in its neural activity. It is reciprocally connected with neu
rons processing sensory information and is thought to be an important sourc
e of top-down influences it exerts on these neurons.
When such
tasks involve comparisons of motion directions separated by a delay, prefr
ontal neurons show direction selective responses that are reminiscent of re
sponses in the motion processing area MT, suggesting that LPFC responses re
present bottom-up signals arriving directly from MT of the same hemisphere.
These neurons are also active during the memory delay and during the compa
rison, reflecting the remembered direction. Furthermore, at the time of per
ceptual decision their activity is highly predictive of the animals’
behavioral report. Thus, the activity recorded in the LPFC during memory-gu
ided comparisons of visual motion suggests a role for this region in the me
mory for motion tasks.
Despite being strongly implicated in se
nsory working memory, the LPFC contribution to this important process is th
e topic of active debate. For years it has been argued that prefrontal cort
ex is the site of sensory storage. However, there is accumulating evidence
that its role is not in the storage of relevant sensory stimuli, but in the
allocation of visual attention to such stimuli and in providing top-down s
ignals to sensory neurons where such signals are likely to be stored. We us
ed unilateral LPFC lesions to examine its role in working memory by measuri
ng coherence thresholds for remembering motion direction at short and long
memory delays. We found that the motion thresholds, intact at shortest dela
ys, were impaired at longer delays but only when stimuli appeared in the he
mifield contralateral to the lesion, the effect particularly pronounced whe
n the task required rapid reallocation of spatial attention. The contralesi
onal nature of the deficits highlights the importance of the interactions b
etween the LPFC and MT during motion comparisons. Because memory impairment
was equally pronounced when the remembered stimuli were at threshold and w
hen they were coherent, it is unlikely that the LPFC is the site of storage
of stimuli giving rise to the remembered direction. It is more likely that
the role of the LPFC in working memory is in accessing this information du
ring the delay and allowing its utilization in the comparison process.