mutisensory integration / attention and spatial awareness (parietal lobe)

Limbic Association area:

Emotional expression and memory formation. This two functions are closely related (the emotional impact of an event influences whether or not will be remembered)

Parietal Lobe in the human brain, main grya

Equivalent of monkeys's Lateral intraparietal area (LIP) in the human cortex Main gyra in Parietal lobe: • Postcentral gyrus: • Supramarginal gyrus • Angular gyrus • *Superior parietal lobule* Postcentral gyrus- primary somatosensory cortex, *Intraparietal sulcus*- (attention)

Anterior (or Frontal) Association area:

Executive functions (judgment, planning for the future, organizing a series of events from memory to prospective action)

Injury to the parietal lobe

Inability to judge spatial relations (object size or arrangements of objects) - *neglect syndromes* •* Hemispatial Neglect* - failure to notice objects in the hemifield contralateral to lesion - failure of attention or representation • *Simultanagnosia *- (bilateral) inability to see multiple objects at once • *Optic Ataxia* - impairment of visually-guided reaching - affected hemifield is generally opposite lesion; inability to use visuospatial information to guide limb movements

association cortical areas (Association cortices)'

Most of the lateral surface of the brain hemispheres are Higher-order Association areas white:primary cortices Pale blue: unimodal association Dark blue: multimodal association (or higher-order association cortices) see slides!!!

Multimodal association areas (Higher-order Association cortices)

Most of the lateral surface of the brain hemispheres are Higher-order Association areas *Posterior Association area*, *limbic Association area*, and *Anterior (or frontal) Association area*

Sequence of information processing is reversed in the Motor cortices

Once sensory information has been integrated, process along multiple streams, analyzed in multiple Multimodal association areas, a decision about what to do with it occurs. If that decision involves a motor action, then information needs to flow High-order Association cortex (Anterior association), to Premotor and finally Primary motor cortex *Primary sensory cortex first to receive sensory info, Primary motor cortex, last to process and execute a motor response*

Premotor cortices:

Planning and Preparation for movement

Principles of Sensory information processing and Association cortex's function:

Sensory information is processed in a series of input streams along several parallel pathways from peripheral receptors through *primary sensory cortices* and *Unimodal association cortex* to the* multimodal association cortex* of the posterior part of the cortical hemisphere: in the Posterior Parietal and Temporal cortices The Posterior Association areas that process sensory information are highly interconnected with the Frontal Association areas responsible for planning motor actions

Synesthesia

Stimulation of one sensory (or cognitive) pathway leads to automatic - involuntary- experiences in a second sensory pathway. Sensory Cross-talk

Spatial cognition or Spatial awareness

Association of contextual information such an Individual's location,, proximity of other people or objects Posterior parietal cortex and other association cortex (Prefrontal cortex, Premotor cortex, Frontal eye field) and Hippocampus are essential to Spatial cognition *Right hemisphere - Particularly important For spatial cognition in humans*

Resting state and Attention Mode

at rest cortex is receiving and processing sensory information from our internal and external environment When we engage in a particular task, our brain changes from *Default Network* at rest to *focused activation* on specific systems that 'demand' attention

Hierarchical model information processing

connections between cortical areas represent stages of information processing. At each step of this stream more complex analysis of the sensory information is achieved Information flows from Primary Areas *->*Unimodal areas *->*Multimodal assoc. areas

Signal transduction in visual cortices

v1→ v2→ v3→ MT or V4 -MT→MST (other dorsal areas) -V4→ IT *V2:* definition of contours, and spatial orientation of contours, binocular disparity, object/background distinction *V3:* global motion (coherent motion) in the visual field, representation of large are of the visual field. Some studies place V3 in the Dorsal stream other do not. *MT*: strong direction sensitivity *V*4: respond to objects of intermediate complexity (simple geometric shapes), color. *IT:* respond to complex objects - Face perception

Parietal Lobe: areas critically involved in selective attention

• *Superior parietal gyra* - include multiple areas (polymodal and also unimodal). Tactile perception, control of action. • *area 5* (which is Somatosensory unimodal) • *Inferior parietal gyra* - visuospatial cognition (area 7) • *Lateral intraparietal area (LIP)* - (inside the Intraparietal sulcus, wall of the sulcus) - Spatial attention, directing eyes movements toward objects of interest - Strongly associated with Neglect syndromes • *Ventral intraparietal area (VIP*) - (inside the Intraparietal sulcus, bottom of the sulcus) - Multimodal Visual, auditory and Somatosensory areas (deep in the sulcus)

Most common synesthesias:

*Grapheme-Color or Color-Grapheme Synesthesia* Letters and numbers are perceived as inherently colored *Chromesthesia:* sound involuntarily evokes an experience of color. In some cases, everyday sounds (people talking or doors opening) can trigger seeing colors. In other cases, seeing colors is triggered by musical notes. *Spatial sequence synesthesia (SSS):* tendency to see numerical sequences as points in space (Number 1 will be farther than away and number 2 will be closer) *Commonly classified as Developmental or Acquired:* Developmental: miss-wiring due to abnormal formation or pruning of connections - mostly in associative areas. Predispose to changes in sensory processing and cognitive functions Acquired: induced by drugs, neurological disorders, thalamic lesions, sensory deprivation, etc

Sensory processing in Somatosensory and Visual cortices (Primary, Unimodal and Multimodal areas)

*somatosensory cortex* -areas 1: process texture -area 2: process size and shape -3a: process propioceptive input -3b: recive most of the discriminative-touch input *posterior parietal cortex* -area 5 -area 7: integrates somatosensory information with other modalities

Posterior Association area:

Is concerned with extrapersonal space (with defining spatial relationships with the world around us), and binding individual elements of a visual scene into a coherent whole scence (visuo-spatial integration)

Primary motor cortex:

execution of movement

attention

*the ability to focus on processing one aspect of sensory inputs* Benefits performance of behavioral tasks: - Enhanced detection Study attention by examining behavioral manifestations, e.g., visual attention - saccade etc

Neglect and Attentional disorder

A person ignore objects, people, sometimes their own body to one side from the center of their visual space (or spatial awareness area) Considered as a manifestation of *unilateral deficit of attention* (makes ignore the other half of the sensory- space) Neglect syndrome is more common following Right parietal lobe damage (which

attention mode

Change from Default mode to focused mode could be induced by: - *Exogenous attention or Bottom-up attention*: A stimulus attracts our attention without any cognitive input (e.g. an object bright color 'pops out' from the background, 'caught our attention'). Triggered by a salient stimulus. - *Endogenous attention or Top-down attention:* Attention is deliberately directed by to some object or place to serve a behavioral goal (flipping quickly through pages of a book looking for a picture that you know is in a corner). Directed by internal expectation

Areas in the Posterior parietal cortex important for Spatial cognition

Extensive representation of peripheral visual field. Involved in Spatial awareness and guidance of movements in our visual space Posterior parietal cortex Specializations for motion detection - Injury to MT can result In loss of motion perception (look at arrow chart girl)

Optical Ataxia:

Impairment of visually-guided reaching of objects • Results from either unilateral or bilateral damage of the Posterior Parietal cortex (damage of the Dorsal stream) • Patient is unable to reach and object in their visual field, however the inability can not be explained by motor, somatosensory, or visual detection deficits

Convergence in Multimodal association areas

Unimodal sensory inputs converge on multimodal association areas in the prefrontal, parietal, temporal and limbic cortices Neurons in these areas respond to combinations of signals representing *different sensory modalities and build an internal representation of the sensory stimulus*

Simultagnosia

inability of an individual to perceive more than a single object at a time • In a complex scene (a table with several objects), the patient will only report seeing one at a time • *Dorsal simultagnosia*: from bilateral lesions in the parietal lobe. Patients are not able to navigate through a space as they bump into other objects, as they are unaware of them. • *Ventral Simultagnosia*: from damage to the left occipito-temporal junction (damage of the ventral stream). Patients are able to see several objects at once, but their recognition is only partia

McGurk effect:

input from one sensory pathway (vision) influencing the perception of the input from another sensory pathway (audition). Sensory Dominance

Unimodal areas:

integrate information from a single sensory modality (e.g. shape, size, texture of an object are processed in unimodal somatosensory cortical areas)

Multimodal areas:

integrate information from more than one sensory system (texture, color, shape, motion, taste, etc.)