| dc.description.abstract | The posterior parietal cortex (PPC), generally refers to the part of parietal cortex posterior to Brodmann’s Areas 3, 1, and 2 of the somatosensory areas, is a prominent feature of primate brains. PPC emerged in early mammals and expanded significantly in humans, marking it as a hallmark of primate cognitive evolution (Goldring and Krubitzer, 2020). A cortical fissure preserved in all primates, the intraparietal sulcus (IPS), commonly serves as an anatomical landmark for PPC. Unlike some cortical areas that can be well characterized by distinctive architectural features, complete representations of the body surface or visual field, or unique neuronal properties, a clear definition of the PPC region remains under debate, especially in anthropoids with enlarged PPC (Cavada, 2001; Hinkley et al., 2010).
PPC has also been termed parietal associative cortex to reflect its role in integration of various sensory modalities, which was facilitated by its location surrounded by visual, somatosensory, and auditory areas.
Mountcastle introduced the ”command function hypothesis,” proposing that functions of PPC include those related to ”acts aimed at certain behavioral goals” (Mountcastle et al., 1975). Accumulating evidence has
indicated that PPC differs from primary sensory or motor cortex, which directly processes input information or controls movements. Instead, investigators argue that PPC plays an essential role in transforming sensory information into perception and generating action plans (Snyder et al., 1997; Andersen, 1997; Batista et al., 1999; Andersen and Buneo, 2002; Cohen and Andersen, 2002). Moreover, PPC contributes to higher-level cognitive functions such as attention, memory, and decision-making (Todd and Marois, 2004; Malhotra et al., 2009; Katsuki and Constantinidis, 2012; Shomstein, 2012; Sestieri et al., 2017; Zhou and Freedman, 2019).
An appreciation of the correlation between structures and functions of PPC can be gained even from a cursory examination of the literature. Complex functions attributed to PPC depend on a cortical structure
connecting multiple modules, as demonstrated by a substantial amount of anatomical work (Hyvarinen, 1982; Andersen et al., 1990; Stepniewska et al., 2009b; Gharbawie et al., 2011; Konen et al., 2013). On the other
hand, focal damage to PPC can result in a wide range of sensorimotor defects, from different forms of apraxia to hemispatial neglect, as evidenced by clinical syndromes in patients (Lynch, 1980; Auerbach and Alexander, 1981; Battaglia-Mayer et al., 2006; Nachev and Husain, 2006; Goldenberg, 2009; Vallar and Calzolari, 2018). Therefore, it is important to have a thorough understanding of PPC from the anatomical perspective to better understand its role regarding different functions and behaviors.
The goal of this dissertation is to expand our knowledge of the functional organization and anatomical connections of PPC. Northern greater galagos (Otolemur garnettii), members of the strepsirrhine radiation
of primates that are generally considered closely resembling early primates that emerged over 60 mya, are used here as the research model for the advantage of their relatively less complex brain while preserving
common features of the primate brain (Kaas, 2013). Findings made in galagos can also provide valuable data for cross-species comparison of the primate PPC, and even suggest some features of human PPC from
an evolutionary perspective. Specifically, Chapter 1 reviews previous works concerning the architecture and connectivity of primate PPC, most of which were conducted on the widely used macaque monkeys, although some studies on other primates and humans are also included for comparison. Chapter 2 reports the features of an identified action-specific zone of PPC as well as its cortical connections. Chapters 3 and 4 describe thalamic connections of the rostral and caudal parts of PPC, respectively. Chapter 5 summarizes the findings in the aforementioned studies and relates these findings to the proposed visual-motor functions of PPC with a general discussion. | |
