this report. Ninety-eight of these cells were recorded from the monkey performing the ABBA task, and 47 were recorded from the monkey performing the standard task.

Previous studies have suggested that both the prefrontal cortex (PFC) and inferior temporal cortex (ITC) are involved in high-level visual processing and categorization, but their respective roles are not known. To address this, we trained monkeys to categorize a continuous set of visual stimuli into two categories, “cats ” and “dogs. ” The stimuli were parametrically generated using a computer graphics morphing system (Shelton, 2000) that allowed precise control over stimulus shape. After training, we recorded neural activity from the PFC and the ITC of monkeys while they performed a category-matching task. We found that the PFC and the ITC play distinct roles in category-based behaviors: the ITC seems more involved in the analysis of currently viewed shapes, whereas the PFC showed stronger category signals, memory effects, and a greater tendency to encode information in terms of its behavioral meaning. Key words: categorization; monkey; vision; object vision; inferior temporal cortex; prefrontal cortex; learning

What we perceive depends critically on where we direct our attention. For example, attention to a location dramatically improves the accuracy and speed of detecting a target at that location. Attention has been shown not only to increase perceptual

We present computer simulations of a model of the brain mechanisms operating in short-term memory tasks that are consistent with the anatomy and physiology of prefrontal cortex and associated subcortical structures. These simulations include dynamical processes in thalamocortical loops which are used to generate short-term persistent responses in prefrontal cortex. We discuss this model in terms of the representation of input stimuli in cortical association areas and prefrontal short-term memory areas. We report on interference phenomena that result from the interaction of these dynamical processes and lateral projections within cortical columns. These interference phenomena can be used to elucidate the representational organization of short-term memory. Introduction Short term persistent response of prefrontal cortex neurons has been postulated as a mechanism for short-term memory (STM) (Fuster, 1989; Goldman-Rakic, 1994). We have previously presented models of STM based upon oscilla...

this article has been on areas of relative decrease, but we also note that, although less troublesome, the same ambiguity in interpretation of regional decreases also holds for regional increases. Activations can arise from either stronger influences on a region or stronger influence of a region. Moreover, the interpretation of the label "activated" or "deactivated" depends greatly on the reference task. Structural equation modeling can aid in distinguishing the several potential sources of changes in rCBF by examining interactions within a task and then allowing comparison of the interactions between tasks (Fig. 4)

You might find this additional information useful... This article cites 99 articles, 38 of which you can access free at:

Attention-dependent modulation of neural activity in visual association cortex (VAC) is thought to depend on top-down modulatory control signals emanating from the prefrontal cortex (PFC). In a previous functional magnetic resonance imaging study utilizing a working memory task, we demonstrated that activity levels in scene-selective VAC (ssVAC) regions can be enhanced above or suppressed below a passive viewing baseline level depending on whether scene stimuli were attended or ignored (Gazzaley, Cooney, McEvoy, et al. 2005). Here, we use functional connectivity analysis to identify possible sources of these modulatory influences by examining how network interactions with VAC are influenced by attentional goals at the time of encoding. Our findings reveal a network of regions that exhibit strong positive correlations with a ssVAC seed during all task conditions, including foci in the left middle frontal gyrus (MFG). This PFC region is more correlated with the VAC seed when scenes were remembered and less correlated when scenes were ignored, relative to passive viewing. Moreover, the strength of MFG--VAC coupling correlates with the magnitude of attentional enhancement and suppression of VAC activity. Although our correlation analyses do not permit assessment of directionality, these findings suggest that PFC biases activity levels in VAC by adjusting the strength of functional coupling in accordance with stimulus relevance.

Regional cerebral blood flow, measured with positron emission tomography, was used to identify brain regions that play a special role(s) in a working memory task for faces. Perceptual matching (no retention interval), short-delay (average = 3.5 s retention interval), intermediate-delay (average- 12.5 s), and long-delay (21 s) tasks were considered. From the idea that brain function is the result of neural interactions, the data were analyzed using anatomically based, covariance structural equation modeling. In perceptual matching, the dominant functional interactions were observed among the ventral cortical areas, from extrastriate regions, to the anterior temporal, and into the inferior prefrontal cortex. These interactions decreased with longer delay intervals. In the short-delay functional model, interactions along this ventral stream in the right hemisphere appeared to be rerouted through limbic areas with strong interactions among the hippocampal region, the anterior and posterior cingulate, and the inferior prefrontal cortices. For the intermediate-delay model, the hippocampocingulate interactions continued, but showed a shift to more left hemisphere involvement In the long-delay network, interactions within the right limbic circuit were reduced in favor of strong bilateral inferior prefrontal and frontocingulate interactions. Effects from the prefrontal cortex, especially from the left hemisphere, to temporal and occipitotemporal cortices were particularly strong in the long-delay model, suggesting recruitment of some of the same circuits primarily involved in face perception. The strong corticolimbic interactions at short and intermediate delays may represent maintenance of an iconic representation of the face during the retention interval. However, at longer delays, where the image was more difficult to maintain, a frontocingulate-occipital network was used that could represent an expanded encoding strategy resulting in a more resilient memory.

Introduction Comparing and contrasting the neural properties of different brain regions can yield important insight into their respective contributions and, hence, the neural circuitry underlying a given function. Take, for example, perceptual categorization, a process fundamental for normal cognition because it gives meaning to our sensory environment. Several recent studies have reported neuronal correlates of visual categories in two interconnected cortical areas involved in visual recognition, memory, and other visual functions: the inferior temporal cortex (ITC) and the prefrontal cortex (PFC) (Vogels, 1999; Freedman et al., 2001, 2002; Nieder et al., 2002; Sigala and Logothetis, 2002). However, the respective roles of these and other brain areas in categorization remain essentially unknown. The PFC and the ITC have been studied by different investigators using different behavioral paradigms, different stimuli, etc., which are confounding factors that render comparisons between t

Modulations of ongoing alpha oscillations predict