Grant Number: 5R01EY013496-05
Project Title: Motivation and Attention in Posterior Cingulate Cortex
PI Information: ASSISTANT PROFESSOR MICHAEL L. PLATT,  platt@neuro.duke.edu 

Abstract: DESCRIPTION (PROVIDED BY APPLICANT): Anatomical, neurophysiological, and neuroimaging evidence suggest that posterior cingulate cortex (CGp) contributes to both motivational and visuospatial processing (Mesulam 1999; Maddock 1999). New neurophysiological data indicate that CGp neurons not only report the spatial coordinates of visually-guided gaze shifts, but also represent their motivational value (McCoy et al. 2003). The timing arid reward-sensitivity of CGp responses, coupled with the observation that CGp dysfunction in humans is associated with both spatial disorientation and mood/anxiety disorders, invite the hypothesis that this limbic area binds motivational salience to visuospatial locations (Mesulam 1999; McCoy and Platt 2004). Furthermore, neurophysiological evidence suggests that motivational and visuospatial information may be computationally bound by CGp in a manner consistent with attention-based models in learning theory (cf. Pearce and hall 1980). This hypothesis raises several important questions. First, do CGp neurons encode the motivational value of visual targets independent of overt orienting? Second, are motivational signals in CGp referenced spatially to the eyes, head, world, or objects? Third, do motivational modulations of neuronal activity in CGp reflect external rewards or the subjective salience of visuospatial targets? And fourth, does activation of CGp functionally bind motivational salience to visuospatial locations? We propose to answer these questions through a combination of behavioral, neurophysiological, and microstimulation studies. Preliminary data suggest that CGp neurons signal the conditional motivational value of visual targets independent of saccades; CGp signals are referenced allocentrically to objects in the world; CGp responses are correlated with subjective preferences for a particular visual target location, rather than the history of rewards associated with that target; and microstimulation in CGp systematically biases orienting towards contralateral space. These data are consistent with the proposed hypothesis that CGp binds motivational salience to locations in visual space. Further microstimulation experiments will be aimed at determining whether the timing with which microstimulation is delivered to CGp systematically influences orienting choices as predicted by reinforcement learning theory. The proposed research is an important step in achieving the broader goal of understanding low the limbic system helps guide visuospatial processing areas to adapt attention dynamically to changing contexts and evolving behavioral goals.

Thesaurus Terms:
attention, cingulate gyrus, motivation, neural information processing, saccade, space perception, visual fixation, visual stimulus
choice, form /pattern perception, neuron, neurophysiology, oculomotor nuclei, stimulus interval, visual perception
Macaca mulatta, behavior test, behavioral /social science research tag, electrophysiology, microelectrode

Institution: DUKE UNIVERSITY
2200 W. Main St.
DURHAM, NC 27705
Fiscal Year: 2006
Department: NEUROBIOLOGY
Project Start: 01-APR-2001
Project End: 31-MAY-2010
ICD: NATIONAL EYE INSTITUTE
IRG: COG

Visual and Saccade-Related Activity in Macaque Posterior Cingulate Cortex

Heather L. Dean¹, Justin C. Crowley^4,5 and Michael L. Platt<sup>1,2,3

1</sup>Department of Neurobiology, ²Center for Cognitive Neuroscience, and ³Department of Biological Anthropology and Anatomy, Duke University Medical Center, Durham, North Carolina 27710; and ⁴Department of Biological Sciences and ⁵Center for the Neural Basis of Cognition, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213

Submitted 17 July 2003; accepted in final form 9 June 2004
J Neurophysiol 92: 3056-3068, 2004

Surgical procedures
A head-restraint prosthesis and scleral search coil (*Fuchs and Robinson 1966 ; Judge et al. 1980 ) were implanted in an initial aseptic surgical procedure performed under isoflurane anesthesia. First, the dorsal rostrum of the skull was exposed and six 2.5-mm holes were drilled through the skull with standard orthopedic surgical instruments. These holes were then tapped for 3.5-mm fine-thread orthopedic cortical bone screws. Sterile orthopedic bone cement (Biomet; Palacos) was used to bond a stainless steel head post (Crist Instruments) lowered to just above the skull surface to 6 titanium screws (Zimmer) inserted into the tapped holes. The Teflon-insulated scleral search coil (Cooner Wire AS634) was implanted beneath the conjunctiva, passing just rostral to the insertions of the extraocular muscles (Judge et al. 1980 ). The wire exited the conjunctiva temporally, exited the orbit subdermally, was embedded in the bone cement that formed the restraint prosthesis, and terminated in a gold and plastic electrical connector (Winchester Electronics/Litton). After surgery, animals received analgesics for a minimum of 3 days. Antibiotic prophylaxis was initiated intraoperatively and continued for 7–10 days. Animals were given a 4- to 6-wk recovery period after surgery.
 
A second aseptic surgical procedure was performed once animals could reliably execute all the behavioral tasks used in the study. A stainless steel recording chamber (Crist Instruments) was positioned stereotaxically perpendicular to the horizontal plane over a 15-mm craniotomy and bonded to 4–6 additional orthopedic bone screws and the original implant with orthopedic bone cement. The recording chamber was centered stereotaxically at position 0,0, the intersection of the midsagittal and interaural planes (cf. Olson et al. 1996 ). Postoperatively, animals received analgesics for a minimum of 3 days and antibiotics for 7–10 days. The recording chamber was kept clean with daily antibiotic washes and sealed with replaceable sterile Cilux caps. Single-cell recording experiments began after a 1-wk postoperative period.

Behavioral techniques
Access to water was controlled during training and testing, and animals were habituated to head restraint and trained to perform oculomotor tasks for a fruit-juice reward using a custom-built software interface (Ryklin Software). Visual stimuli consisted of light-emitting diodes (LEDs; LEDtronics), which could be illuminated to appear red, green, or yellow to normal human observers. The LEDs were fixed on a tangent screen placed 144.78 cm (57 in.) from the eyes of the animal, forming a grid of points, separated by 1°, spanning 49° horizontally and 41° vertically. These LEDs could be illuminated within 1 ms and extinguished within 7 ms by the computer system controlling the experiments.

* Fuchs and Robinson 1966