Electrical recordings in humans and monkeys show attentional enhancement of evoked responses and gamma synchrony in ventral stream cortical areas. Does this synchrony result from intrinsic activity in visual cortex or from inputs from other structures? Using paired-recordings in the frontal eye field (FEF) and area V4, we found that attention to a stimulus in their joint receptive field leads to enhanced oscillatory coupling between the two areas, particularly at gamma frequencies. This coupling appeared to be initiated by FEF and was time-shifted by about 8-13 ms across a range of frequencies. Considering the expected conduction and synaptic delays between the areas, this time-shifted coupling at gamma frequencies may optimize the postsynaptic impact of spikes from one area upon the other, improving cross-area communication with attention.

We traced the cortical connections of the 4 cytoarchitectonic fields--Opt, PG, PFG, PF--forming the cortical convexity of the macaque inferior parietal lobule (IPL). Each of these fields displayed markedly distinct sets of connections. Although Opt and PG are both targets of dorsal visual stream and temporal visual areas, PG is also target of somatosensory and auditory areas. Primary parietal and frontal connections of Opt include area PGm and eye-related areas. In contrast, major parietal and frontal connections of PG include IPL, caudal superior parietal lobule (SPL), and agranular frontal arm-related areas. PFG is target of somatosensory areas and also of the medial superior temporal area (MST) and temporal visual areas and is connected with IPL, rostral SPL, and ventral premotor arm- and face-related areas. Finally, PF is primarily connected with somatosensory areas and with parietal and frontal face- and arm-related areas. The present data challenge the bipartite subdivision of the IPL convexity into a caudal and a rostral area (7a and 7b, respectively) and provide a new anatomical frame of reference of the macaque IPL convexity that advances our present knowledge on the functional organization of this cortical sector, giving new insight into its possible role in space perception and motor control.

Summary Shifts of gaze and shifts of attention are closely linked and it is debated whether they result from the same neural mechanisms. Both processes involve the frontal eye fields (FEF), an area which is also a source of top-down feedback to area V4 during covert attention. To test the relative contributions of oculomotor and attention-related FEF signals to such feedback, we recorded simultaneously from both areas in a covert attention task and in a saccade task. In the attention task, only visual and visuomovement FEF neurons showed enhanced responses, whereas movement cells were unchanged. Importantly, visual, but not movement or visuomovement cells, showed enhanced gamma frequency synchronization with activity in V4 during attention. Within FEF, beta synchronization was increased for movement cells during attention but was suppressed in the saccade task. These findings support the idea that the attentional modulation of visual processing is not mediated by movement neurons.

It is widely held that the frontal eye field (FEF) in prefrontal cortex (PFC) modulates processing in visual cortex with attention, although the evidence for a necessary role is equivocal. To help identify critical sources of attentional feedback to area V4, we surgically removed the entire lateral PFC, including the FEF, in one hemisphere and transected the corpus callosum and anterior commisure in two macaques. This deprived V4 of PFC input in one hemisphere while keeping the other hemisphere intact. In the absence of PFC, attentional effects on neuronal responses and synchrony in V4 were significantly reduced and the remaining effects of attention were delayed in time indicating a critical role of PFC. Conversely, distracters captured attention and influenced V4 responses. However, because the effects of attention in V4 were not eliminated by PFC lesions, other sources of top-down attentional control signals to visual cortex must exist outside of PFC.

The ability to select information that is relevant to current behavioral goals is the hallmark of voluntary attention and an essential part of our cognition. Attention tasks are a prime example to study at the neuronal level, how task related information can be selectively processed in the brain while irrelevant information is filtered out. Whereas, numerous studies have focused on elucidating the mechanisms of visual attention at the single neuron and population level in the visual cortices, considerably less work has been devoted to deciphering the distinct contribution of higher-order brain areas, which are known to be critical for the employment of attention. Among these areas, the prefrontal cortex (PFC) has long been considered a source of top-down signals that bias selection in early visual areas in favor of the attended features. Here, we review recent experimental data that support the role of PFC in attention. We examine the existing evidence for functional specialization within PFC and we discuss how long-range interactions between PFC subregions and posterior visual areas may be implemented in the brain and contribute to the attentional modulation of different measures of neural activity in visual cortices.

The inferior parietal lobule (IPL) of the macaque monkey constitutes the largest part of Brodmann's area 7. Functional, connectional, and architectonic data have indicated that area 7 is comprised of several distinct sectors located in the lateral bank of the intraparietal sulcus and on the IPL cortical convexity. To date, however, attempts to parcellate the IPL based on architectonic criteria have been controversial, and correlation between anatomical and functional data has been inadequate. In the present study we aimed to determine the number and extent of cytoarchitectonically distinct areas occupying the IPL convexity. To this end, we studied the cytoarchitecture and myeloarchitecture of this region in 28 hemispheres of 17 macaque monkeys. Four distinct areas were identified at different rostrocaudal levels along the IPL convexity and were defined as PF, PFG, PG, and Opt, with area PF corresponding to the rostralmost area and area Opt to the caudalmost one. All areas extend dorsally up to the lateral bank of the intraparietal sulcus, for about 1-2 mm. Areas PF, PFG, and PG border ventrally on opercular areas, whereas area Opt extends ventrally into the dorsal bank of the superior temporal sulcus. Analysis of the distribution of SMI-32 immunoreactivity confirmed the proposed parcellation scheme. Some additional connectional data showed that the four areas project in a differential way to the premotor cortex. The present data challenge the current widely used subdivision of the IPL convexity into two areas, confirming, but also extending the subdivision originally proposed by Pandya and Seltzer.

We used the [14 C]-2-deoxyglucose method to study the location and extent of primate frontal lobe areas activated for saccades and fixation and the retrograde transneuronal transfer of rabies virus to determine whether these regions are oligosynaptically connected with extraocular motoneurons. Fixation-related increases of local cerebral glucose utilization (LCGU) values were found around the fundus of the inferior limb of the arcuate sulcus (AS) just ventral to its genu, in the dorsomedial frontal cortex (DMFC), cingulate cortex, and orbitofrontal cortex. Significant increases of LCGU values were found in and around both banks of the AS, DMFC, and caudal principal, cingulate, and orbitofrontal cortices of monkeys executing visually guided saccades. All of these areas are oligosynaptically connected to extraocular motoneurons, as shown by the presence of retrogradely transneuronally labeled cells after injection of rabies virus in the lateral rectus muscle. Our data demonstrate that the arcuate oculomotor cortex occupies a region considerably larger than the classic, electrical stimulation-defined, frontal eye field. Besides a large part of the anterior bank of the AS, it includes the caudal prearcuate convexity and part of the premotor cortex in the posterior bank of the AS. They also demonstrate that the oculomotor DMFC occupies a small area straddling the ridge of the brain medial to the superior ramus of the AS. Our results support the notion that a network of several interconnected frontal lobe regions is activated during rapid, visually guided eye movements and that their output is conveyed in parallel to subcortical structures projecting to extraocular motoneurons.

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