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How does the brain organize its work? And how does it heed what it needs to heed? Theories of brain organization focus on two distinct but complementary principles of brain organization: modularity, the existence of brain regions with specialized functions, and network connectivity, the integration of information from various brain regions that results in organized behavior. In the study under review here, the modular and network models appear to play specialized roles in directing the attention of monkeys seeking certain visual targets through either "top-down" or "bottom-up" attentional strategies. Modules versus networks In the modules-versus-network debate, modularity is probably the simpler brain model to understand. Clinical observation of individuals with brain damage, as well as brain-imaging studies (functional MRIs, or fMRIs) of healthy individuals, demonstrate that certain brain regions control specific cognitive processes, such as the ability to produce speech. For instance, in patients with nonfluent aphasia, which creates a selective inability to speak, comprehension of spoken language remains intact. In 1861 Paul Broca observed that damage to the left frontal lobe in an autopsied brain had produced nonfluent aphasia. Modern brain-imaging studies of patients with strokes to this area (now known as "Broca's area") confirmed Broca's theory. Moreover, fMRIs of healthy individuals reveal that the left frontal lobe is activated when subjects generate speech. Of course, that some brain areas specialize in certain functions does not exclude the possibility that those areas are also part of larger networks of brain regions communicating with one another. Although the modular model may accurately describe many cognitive functions, it is insufficient to explain complex cognitive processes that cannot be localized to isolated brain regions. It is unlikely that our ability to get the gist of a conversation, for instance, is the work of a single specialized brain module. Such complex behavior more likely arises from interactions between brain regions through network connectivity. In his 1995 book Memory in the Cerebral Cortex: An Empirical Approach to Neural Networks in the Human and Nonhuman Primate, UCLA neurologist Joaquin Fuster began an argument he extended in his 2002 work Cortex and Mind: Unifying Cognition. According to Fuster, new studies of brain networks have led to a "revolution in contemporary neuroscience." He contends that the empirical shift from a reductionist modular model to a holistic network model offers promise of accomplishing our long-term goal of resolving the mind-brain question. Fuster's conception of a network model of brain function includes several key notions: (1) Cognitive information is represented in wide, overlapping and interactive brain networks. (2) Such networks develop on a core of organized modules of elementary sensory and motor functions, to which they remain connected. (3) The cognitive code is a relational code, based on connectivity between discrete brain regions. (4) The code's diversity and specificity derive from the myriad possible combinations of those brain regions. (5) Any brain region can be part of many networks and thus of many percepts, memories, items of experience or personal knowledge. (6) A given brain network can serve several cognitive functions. (7) Cognitive functions consist of functional interactions within and between brain networks.

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