Understanding the parietal lobe syndrome from a neurophysiological and evolutionary perspective

Abstract

In human and nonhuman primates parietal cortex is formed by a multiplicity of areas. For those of the superior parietal lobule (SPL) there exists a certain homology between man and macaques. As a consequence, optic ataxia, a disturbed visual control of hand reaching, has similar features in man and monkeys. Establishing such correspondence has proven difficult for the areas of the inferior parietal lobule (IPL). This difficulty depends on many factors. First, no physiological information is available in man on the dynamic properties of cells in the IPL. Second, the number of IPL areas identified in the monkey is paradoxically higher than that so far described in man, although this issue will probably be reconsidered in future years, thanks to comparative imaging studies. Third, the consequences of parietal lesions in monkeys do not always match those observed in humans. This is another paradox if one considers that, in certain cases, the functional properties of neurons in the monkey's IPL would predict the presence of behavioral skills, such as construction capacity, that however do not seem to emerge in the wild. Therefore, constructional apraxia, which is well characterized in man, has never been described in monkeys and apes. Finally, only certain aspects, i.e. hand directional hypokinesia and gaze apraxia (Balint's psychic paralysis of gaze), of the multifaceted syndrome hemispatial neglect have been described in monkeys. These similarities, differences and paradoxes, among many others, make the study of the evolution and function of parietal cortex a challenging case.

Functional Rather than Effector-Specific Organization of Human Posterior Parietal Cortex

“…Previous studies have demonstrated a caudo-rostral gradient in PPC responses when comparing movement planning for saccades and hand movements in monkeys (Burnod et al, 1999;Caminiti et al, 2010) and humans (Astafiev et al, 2003;Connolly et al, 2003;Medendorp et al, 2005;Beurze et al, 2007Beurze et al, , 2009Connolly et al, 2007;Filimon et al, 2009). The current study confirms those findings, but also indicates that they cannot be interpreted as evidence for effector-specific, somatotopic organization of PPC (Chang et al, 2008;Andersen and Cui, 2009).…”

“…To conclude, we report that PPC is organized according to a caudo-rostral visual-to-somatic gradient in PPC (Burnod et al, 1999;Beurze et al, 2007Beurze et al, , 2009Levy et al, 2007;Caminiti et al, 2010). Contrary to common view, this gradient does not seem to reflect effector specificity beyond a crude distinction between eye movements and movements of other body parts.…”

“…Center coordinates (given in Talairach coordinates) for the indicated areas were chosen according to previous reports (see Materials and Methods; Table 1). portion of the SPL could therefore specify the effector-specific motor plan together with frontal motor areas, including M1 and the premotor cortex (Caminiti et al, 2010).…”

“…In both humans and nonhuman primates, different portions of the PPC are preferentially active for preparing different types of actions or for movements involving different body parts (Hyvärinen, 1981;Murray and Coulter, 1981;Graziano and Gross, 1998;Andersen and Cui, 2009;Caminiti et al, 2010). In the intraparietal sulcus (IPS) of macaques, neurons in the lateral intraparietal area (LIP) respond preferably during the planning of saccades, whereas neurons in the adjacent parietal reach region (PRR) respond more strongly during arm reach planning (Calton et al, 2002;Cui and Andersen, 2007;Andersen and Cui, 2009).…”

Right Hand Predominant Constructional Apraxia due to Right Hemisphere Infarction without Corpus Callosum Lesions

“…This condition can be caused by either the failure to effectively analyze the spatial structure of a model (perceptual function) or coordinate motor output to reproduce the structure through a sequence of actions (motor function) (2). Whether the former or latter is related to the failure in reproducing visual figures is usually unclear in each patient in clinical practice; therefore, the more general term "constructional disability" is also used to describe this condition.…”