Parietal lobes

Central sulcus (rolandic fissure)

• Separates frontal and parietal lobes.

Lateral sulcus

Separates temporal lobe from parietal and frontal lobes

Pareto-occipital fissure

Divided occipital and parietal lobes

Postcentral gyrus

• In between the central and postcentral sulcus.

• Receives somatosensory information from the entire body.

Posterior parietal lobes

• Superior parietal lobule (SPL; little lobe)

• Inferior parietal lobe (IPL)

• In between these two is the intraparietal sulcus (IPS) which is a major sulcus.

Intraparietal sulcus (IPS)

Summary of major antamoical subdivisions

• Postcentral gyrus

• Posterior parietal lobe (superior lobule

Summary of major functional subdivisions

- Primary somatosensory cortex (S1)
- Posterior parietal cortex: infraparietal sulcus and superior parietal lobule, right inferior parietal lobule, left anterior inferior parietal lobule, left posterior inferior parietal lobule.

Primary somatosensory cortex (S1)

• Processing information about body sensations (e.g. touch, pain, proprioception)

• Can be divided into at least 4 subdivisions (area 3a, 3b, 1 and 2)

• Input: mainly from thalamus and motor cortex

• Output: mainly to motor cortex and posterior parietal cortex.

Wilder Penfield (1930s to 50s)

• Noted that some body parts have a larger dedicated area than others

• Also known at the somatosensory homunculus

Why somatotopy is more complex

While there is clear somotatopy, it is not as simple as depicted by penfield,

Somatosensory cortex study (Kolansinski et al., 2016)

• Our brain more wired than we assume, functional reoroganisation of S1 can occur within just 24 hours.

• Kolansinski et al., showed this by an experiment where the little finger and ring finger were glued together.

Intrapariteal sulcus and superior parietal lobule

Visually guided actions.

Overarching concept

Vision for action - dorsal visual stream (Goodale, 2011, Ganel and Goodale, 2018)

• Is there an object with which I can interact? What is its size and orientation?       Objects in space, object relevance / attention.

• Where is my body (arms, hands, eyes, finger) relative to the object?       Reaching / grasping objects.

• More anterior areas – coding in hand-centred coordinate system.

• More posterior areas – coding in vision-centred coordinate system (retinotopy).

Classic neuropsychological sydndrome after bilateral lesions

Balint syndrome (Jackson et al., 2009)

• Optic ataxia: deficit in visually guided reaching movements (Anderson et al., 2014)

• Oculomotor apraxia: inappropriate fixation of gaze and difficulties in voluntarily shifting fixation to other objects.

• Simultanognosia: impaired ability to perceive multiple items in a visual display.

Involvement in cognitive functions might derive from more primitive mechanisms

• Visuospatial working memory: link to representing the location of objects, coding what is relevant.

• Mental rotation/imagery: link to manipulating objects.

• Arithmetics: link to moving eyes/hands to count, spatial layout (mental number line).

Right inferior parietal lobule

• Detect salient events in the environment

Singh-Curry & Hussain (2009)

• Detection and encoding of salient or novel events (bottom up attention, ie. up from stimuli via senses- brain interprets.

• Key role in maintaining attention on current task goal as well as encoding of salient events so that task sets can be speedily reconfigured to deal with new challenges.

Left anterior inferior parietal lobe

Use objects in appropriate way, pantomime object use.

Left posterior inferior parietal lobule

Detect salient events in one’s thoughts.

Seghier (2012)

• Semantic processing

• Reading and comprehension

• Default mode processing

• Number processing

• Memory retrieval

• Theory of mind

Reynaud et al. (2016)

• Understanding tool-use actions

• Lesions in this area - Apraxia with possible impairments

• Imitation of gestures

• Communicative gestures

• Real tool use.