L+Gyrus+Cinguli

=Posterior Gyrus cinguli= == Chapter 8, p.127

Despite the fact that early hypometabolism and neural degeneration in posterior cingulate cortex (CGp) predict cognitive decline in Alzheimer ’ s disease, and CGp hyperactivity predicts cognitive dysfunction in schizophrenia as well as fi rst-degree relatives, the function of this brain area remains unclear. The disparate evidence for CGp involvement in a variety of cognitive and behavioral processes has belied any simple functional description. Here we develop a new model that proposes that CGp integrates the recent history of rewards, errors, volatility, and context for the purpose of detecting changes in the environment and signaling the need for consequent changes in behavioral policy. In this model, suppressed CGp activity favors operation within the current behavioral policy and cognitive set, with few “ open channels ” for information to gain access to cognition and behavior. By contrast, increased CGp activity refl ects a change in large-scale environmental contingencies or internal state and promotes fl exibility, exploration, and renewed learning. In light of this new hypothesis, we review known electrophysiological responses of single neurons in CGp, and discuss the relationship of our model to the role of CGp in the so-called default mode of resting state activity.

The Basics: Anatomy and Physiology of CGp
Cingulate cortex, within the depths of the cingulate sulcus as well as along the medial wall of the cingulate gyrus, has long been recognized as an important site integrating sensory, motor, visceral, motivational, emotional, and mnemonic information. 44,60 Electrical microstimulation of various regions within cingulate cortex can evoke visceral or “ emotional ” responses, such as changes in heart rate or blood pressure, as well as vocalizations and movements of the limbs, 39,75,79,87 and can support self-stimulation behavior. 63 Neurophysiological studies in animals indicate that neurons in CGp respond to both sensory events 16,17,58 and the motivational and informational signifi cance of those events. 20,34,47,62 Humans with posterior cingulate dysfunction may show emotional disturbances, such as schizophrenia and obsessivecompulsive disorder, 18 spatial impairments similar to the defi cits of patients with parietal lesions, or memory deficits. In addition to its prominent reciprocal anatomical connections with areas involved in spatial attention — areas 7a, LIP, and 7, or PGm 1,2,6,9,53,59,83 — CGp is also strongly connected with brain areas known to be involved in learning and motivation, and to areas sensitive to reinforcement contingencies, including the anterior and lateral thalamic nuclei, 22 the caudate nucleus, 2,64,91 and orbitofrontal cortex. 2,54,59 In addition, CGp is strongly and reciprocally interconnected with anterior cingulate cortex (ACC), which contains neurons carrying nociceptive 73 and reward-related information, 35,57,72 and is capable of engaging reinforcement-related circuitry when artifi - cially activated. 28,76 Finally, numerous neuroimaging studies in humans have linked CGp to the socalled default network of cortical areas, including ventromedial prefrontal cortex and CGp, which show high metabolic and hemodynamic activity while at rest that is suppressed during active task engagement. 30,66,67 Activation in the default network is anticorrelated with activation of the dorsal frontoparietal network, a set of brain areas implicated in selective attention, and its concomitant benefi ts in accuracy and task performance. 10,19,38 Deactivation of the default network has been implicated in attention, arousal, and task engagement, and increases in hemodynamic response in these areas predict occasional lapses in attention, 89 failures to encode memories, 13 and failures to perceive near-threshold sensory stimuli. 7 Variations in the activity of the default network have been linked to self-directed cognition, 30,49 environmental monitoring, 45 and motivated behavior. 65 Monkeys show strikingly similar patterns of intrinsic metabolic activity within this network, 81 and tonic fi ring rates of single neurons in CGp predict variations in reaction times and error rates within a single task. 36 These data suggest that the default network in general, and CGp in particular, may track moment-to-moment variations in the balance of exteroceptive vigilance and interoceptive cognition needed to monitor the external environment and internal milieu. Recent work suggests that other brain areas, in particular cortical areas lying along the midline, also contribute to conditioning and other types of associative learning. The orbitofrontal and anterior cingulate cortices (OFC and ACC) receive dopaminergic projections and maintain strong reciprocal connections with other structures in the basal ganglia. 31,32 Several hypotheses suggest that these areas are necessary for maintaining representations of and deciding among outcomes, actions, or cues, 41,69,70 as well as facilitating changes in action. 86 Areas such as the dorsolateral prefrontal cortex (DLPFC) are then thought to incorporate these representations into the process of strategic decision making and action planning. 3,42