UE Healthy Reach & Grasp

- Point

- Reach

- Grasp

- Throw

what are the aspects of the task constraint that affects UE ADL function

- Visual

- Somatosensory

- Vestibular

what are the 3 sensory components of reach and grasp

1. Locate Target "Visual Regard"

2. Reach

3. Grasp

4. Manipulate

5. Release

what are the 5 phases of reach and grasp tasks

Neonate

at what age do we develop the ability to Locate Target "Visual Regard" for reach and grasp tasks

Neonate

at what age do we develop the ability to reach for reach and grasp tasks

~4 months

at what age do we develop the ability to grasp for reach and grasp tasks

~12 months

at what age do we develop the ability to manipulate objects for reach and grasp tasks

locate the target

what is the first phase of reach and grasp tasks

space

localization

Key aspects of being able to locate a target for reach and grasp tasks

- Localizing objects in ____

- Factors determining nature and quality of _______

Coordination of eye + head + trunk

what is needed for Localizing objects in space

neck

eyes

inertia

When localizing objects in space through the coordination of eye + head + trunk, ____ muscles are activated first. The ____ will also move first with the lowest _____

Neck muscles activate first

When localizing objects in space for reach and grasp tasks, what muscle activates first

Eyes move first

when localizing objects in space for reach and grasp tasks, what body part moves first

the eyes require lower inertia to move allowing them to move before the neck

despite the neck muscles activating first when localizing objects in space, why do the eyes move before the neck?

- Location in visual field (foveation)

- Level of precision

- Musculoskeletal considerations (age)

in reach and grasp tasks, what 3 factors determine the nature and quality of localization

foveation

high precision

“Level of precision" while locating a target for reach and grasp

- Higher precision tasks require _____ in center of visual field.

- Head moves 60-75% of the way unless ___ ____ is required

eyes

smooth pursuit

saccades

eye control

Situations where the object is directly in front of you (your central vision).

• You don’t need to move your head or body

• Your ____ alone do the work

• Two key eye movements:

  • _______: tracking a moving object (like following a ball)

  • _______: quick jumps between points (like reading or scanning)

In rehab: therapists may train ________ first, since it’s the most basic level of coordination.

vision

neck

VOR

gaze

Eyes + Head

Here, the target is slightly off to the side, so just moving your eyes isn’t enough.

• You move your head, but still keep your eyes locked on the object

• This requires coordination between:

  • ____

  • _____ movement

  • The _____ reflex (VOR) (keeps your gaze stable while your head moves)

In rehab: patients practice ____ stabilization, which is crucial for balance and accurate reaching

eyes

head

trunk/body

whole body

Eyes + head + trunk

This is for objects that are far to the side or outside your immediate field of view.

• You need to move:

  • ____ (to locate)

  • ____ (to orient)

  • _____ (to fully align and reach)

• This is ______ coordination

In rehab: this level is often hardest and most functional (real-life tasks like grabbing something off a shelf or to your side)

Perceptual loss vs. sensory loss

what is Hemineglect vs. Hemianopsia

reaching

what is the second phase of reach and grasp tasks

- Parietal cortex and premotor cortex

- Primary motor (M1) and supplementary motor area (SMA)

- Basal ganglia

- Cerebellum

what 4 areas of the brain contribute to reach and grasp tasks

- Visual-motor transformations

- Formation of movement plan

what is the role of the parietal cortex and premotor cortex in reach and grasp tasks

- Receives movement plan and orchestrates muscle activation

- Higher centers in cortex make movement plan

what is the role of the Primary motor (M1) and supplementary motor area (SMA) in reach and grasp tasks

movement plan

self-initiated

Bradykinesia

Basal Ganglia contribute to reach and grasp tasks

- Receives ______ and makes refinements

- SMA to Putamen – _____ movement

- _____ – Parkinson’s Disease affects slowness of volitional reach/grasp, but not reflexive catch

sensory

motor cortex and brainstem

Cerebellum contribute to reach and grasp tasks

- Receives and updates movement plan with _____ information

- Sends updated movement plan back to _____ and ______

- Predictive control of grip forces, esp. timing

Parietal

Temporal

1. Dorsal Stream: Visual → _____ cortex

2. Ventral Stream: Visual → _____ cortex

"Vision for action" or "WHERE pathway"

What is the Dorsal Stream: Visual → Parietal cortex

Localization

what is the function of the Dorsal Stream: Visual → Parietal cortex

Optic ataxia

what may happen if there is damage to the Dorsal Stream: Visual → Parietal cortex

"Vision for perception" or "WHAT pathway"

what is the Ventral Stream: Visual → Temporal cortex

Perceptual interaction with memory for object identification and object orientation knowledge.

what is the function of the Ventral Stream: Visual → Temporal cortex

Agnosia

what may happen as a result of damage to the Ventral Stream: Visual → Temporal cortex

Ebbinghaus Illusion

It’s a visual illusion where a circle looks bigger or smaller depending on the circles around it:

• A circle surrounded by small circles looks bigger

• A circle surrounded by large circles looks smaller

Even if the two central circles are actually the same size.

action system is NOT fooled

Ebbinghaus Illusion: Dorsal Stream (Action) Results — What your hand does when you reach out to grab the discs:

• “Maximal grip aperture recorded mid-reach”
  → Researchers measured how wide your fingers open while reaching.

• “Small disc in a small annulus estimated as smaller…”
  → Consciously, the illusion still affects you (you think one is smaller).

• “Accurate estimate of disc size”
  → But your hand movement is correct — your fingers open to the real size.

perception system is fooled

Ventral Stream (Perception) Results — What you consciously see

• “Manual estimate of disc size”
  → Participants used their fingers or judgment to indicate size.

• “Small disc in small annulus estimated to be the same as large disc…”
  → The illusion distorts perception — they judge incorrectly.

• “Inaccurate estimate of disc size”
  → Their conscious perception is wrong

longer; slower

grasp

Differences in reaching with and without vision

- With vision → duration ____; velocity ____

- _____ component not altered during reaching without vision.

Grasp component

what component of reach and grasp is unaltered due to lack of vision

visual field

opposite hemispheres

Contralateral reaching more difficult

- Ipsilateral reach faster and more accurate than contralateral - same ______

- Contralateral activities require more time for signals to reach since motor and vision occur in ________

contributes to speed and accuracy

what is the Role of Visual Feedback in reach and grasp

• Proprioception

• vision

• motor programs

Results of the Deafferentation studies with monkeys for determining if somatosensation / proprioception is necessary for reach

• _______ helps, but it’s not absolutely required for movement.

• The brain can:

  • Use ______ as a backup system

  • Rely on stored ________ for familiar actions (even with vision gone)

vision

proprioception

complex movements

• Vision can partially compensate for lost body sense—but if both are gone, movement control breaks down

Human studies using patients with severe neuropathy for determining if somatosensation / proprioception is necessary for reach

When movements are complicated (like reaching around obstacles), patients must rely on _____ to guide their actions.

• Without _____, they don’t know where their limbs are in space.

• So if they also can’t see (eyes closed), they basically lose the ability to perform _______

accurate

Human studies using patients with severe neuropathy for determining if somatosensation / proprioception is necessary for reach

Even for simple movements (like repeatedly reaching to the same spot), patients can initially do okay—but:

• Over time, their movements become less _____ (“drift”)

• Errors accumulate because they can’t internally correct their position

Meaning: Without proprioception, the brain can’t maintain a stable sense of limb position across repeated actions

somatosensory

somatosensory

Human studies using patients with severe neuropathy for determining if somatosensation / proprioception is necessary for reach

Small corrections during movement—like adjusting your hand slightly to hit a target—depend heavily on ______ feedback.

• Vision is slower and less precise for these micro-corrections

• Proprioception provides real-time, continuous feedback

Meaning: Even if vision helps guide the general movement, fine-tuning requires ______ input

Somatosensory

_______ feedback contributes the most at end-range and final phases of reach/grasp

Cutaneous afferents

________ = sensory nerves in the skin that detect touch, pressure, and slip.

• These signals tell your brain things like:

  • How hard you’re holding something

  • Whether it’s slipping

  • The texture and shape

Without this feedback, your brain is basically “guessing” how much force to use.

gripping

If your fingers are numb (e.g., local anesthesia), you can’t feel the object well. So your brain compensates by _____ harder than necessary to avoid dropping it.

memory

Even if you’ve handled the object before (so you “know” how heavy or slippery it is), you still struggle. That’s because ____ alone isn’t enough—you need real-time sensory feedback to fine-tune grip. Grip control is dynamic, not just based on prior experience

touch

______ is more precise than vision for grip control

rapidly

slowly

both

Somatosensory cortex with grip

- Grip onset: brief activation of _____ adapting neurons

- Holding phase: continuous activity of _____ adapting neurons

- Slip response: strong activation of ____ neuron types

- Postural support - axial muscle tone

- Orientation in space (otoliths)

- Perception of self motion

based on research, what are the suggested contributions of the vestibular system to reach and grasp tasks

- Vestibulocolic reflex: neck muscles stabilize head

- Vestibulospinal reflex: trunk muscles stabilize head

how does postural support from axial muscle tone by the vestibular system contribute to reach and grasp (what 2 reflexes are used)

Otoliths and canals

what parts of the vestibular system are involved in Orientation in space and Perception of self-motion

Oscillopsia

what can happen to reach and grasp if the vestibular system is damaged

Oscillopsia

impaired accuracy in reaching to target when eyes are involved; target appears to bounce; impaired VOR.

slowly

visual and proprioceptive

slowly

People with Unilateral Vestibular Loss tend to reach more _____ than healthy individuals. They rely more on _____ and ______ feedback. UVL patients also move their heads more _______ during tasks to reduce dizziness.

M1

Single ____ neuron may innervate several hand muscles. Muscles are activated by multiple of these neurons dispersed throughout cortical hand area.

preferred direction

M1 Activity and Movement Direction monkey experiment

Individual neurons in M1 are not random—they tend to fire most strongly when a movement goes in a specific direction.

• For example, one neuron might fire most when the monkey reaches up and to the right

• The same neuron will still fire for other directions, but less strongly

This is called a “_________” and is often represented as a tuning curve.

redundancy and flexibility

M1 Activity and Movement Direction monkey experiment

Many neurons can share similar preferred directions.

• You don’t have just one neuron for “move right”. Instead, lots of neurons respond to similar directions, but each with slightly different tuning

This overlap creates ____ and _____ in movement control

population coding

M1 Activity and Movement Direction monkey experiment

Movement isn’t controlled by a single neuron—it comes from the combined activity of many neurons.

• Each neuron “votes” for a direction based on how strongly it fires. The brain combines these signals into a population vector. The final movement direction is the result of this combined activity

This is known as ________

muscle force

As firing rate of M1 neurons increases, _______ increases

at 1 week

when do infants reach

power

holding a hammer requires which type of grasp

power grasp

Name the grasp type

• The object is held against the palm

• All fingers wrap around it (often with the thumb reinforcing)

• Generates high force, but not very precise

Precision grasp

Name the grasp type

• Object is held between the fingertips, especially thumb and index finger

• Minimal or no involvement of the palm

• Produces low force, but very high precision

Successful grasp

Name the grasp type

- Adapt to size and shape

- Appropriate timing and force of finger closure relative to transport

1. Contact

2. Begin loading

3. Load force overcomes weight of object.

4. Decrease in grip/load force after contact with target surface.

what are the 4 Phases of Grasp & Lift

begin loading phase

This phase happens right after your fingers make contact but before the object leaves the surface

Pacinian corpuscles

________ are sensory receptors in your skin that respond to vibration and rapid changes. When an object starts to slip, tiny vibrations occur. These receptors detect that immediately. They send signals to your brain → “tighten grip now!”

Feedforward

______ (anticipatory control)

• Your brain predicts how much force is needed before lifting

• Based on past experience (memory of similar objects)

• Happens very fast, without waiting for sensory input

Example: You pick up a coffee mug and already know roughly how heavy it is.

Feedback

______ (reactive control)

• Adjustments made after sensory input comes in

• Uses touch receptors (like Pacinian corpuscles)

• Corrects errors (e.g., slipping, too much force)

Example: If the mug starts slipping, you quickly tighten your grip.

Object starts to move

what happens when Load force overcomes weight of object during grasp and lift tasks

manipulation

what is the fourth phase of reach and grasp tasks

manipulation

_______ is not just grabbing—it’s what happens after the grasp.

• You change how your fingers contact the object

• You reposition it for stability or function

• You coordinate finger position with the object’s shape and orientation

stereognosis

precision

Manipulation is necessary for _____ and _____ grip

release

what is the fifth phase of reach and grasp tasks

opening of the hand by reduction of force applied to the object in the grip.

what does the release phase for reach and grasp tasks entail

If release cannot be performed, the hand cannot be used effectively (i.e. for ADLs).

why is release an important part of reach and grasp tasks

digits

flexion/extension

Release is achieved during reach and grasp tasks by active movement of _____ away from thumb. It also involves passive ____/_____ of wrist

transport

visual

anticipatory control affects the hand during the _____ phase, and ____ info enables anticipation

- Intrinsic: size, shape, texture

- Extrinsic: orientation, distance, location

- Cognitive: experience, learning, dual-task/distraction

What properties of objects affect anticipatory control?

Transport phase

As your hand moves toward an object, it starts to open up.

• Bigger object → wider hand opening

• Smaller object → smaller hand opening

fingers

Transport phase

Most of the fine tuning happens with the _____, not the thumb.

• Fingers spread or close to match object size

• Thumb stays relatively steady and acts like an anchor

75-80%

Transport phase

• Early movement → hand opens gradually

• Mid movement → still adjusting

• Around ____-____% of the way to the object, the hand reaches its maximum opening size

• Then it starts closing slightly to prepare for grasp

thumb and fingers

Final grasp during the transport phase involves _____ and _____

Maximize efficiency

How is anticipation important for function of reach and grasp?

movement speed

Increased postural demand → decreased _________

Cerebellum

______ plays a key role in anticipatory postural adjustments needed for reach and grasp

- Scapular

- GH joint

what 2 types of proximal control and stability is needed for reach and grasp

- Scapula

- GH joint

- Elbow

- Wrist and finger joint mobility

What 4 joints require mobility throughout the UE for reach and grasp tasks

- Lack of use, injury, arthritis, denervation

- Increases inertial forces with movement

- More effort required to control body segment

- More force & power → greater risk of injury

- Reduce movement speed

what is the role of stiffness in reach and grasp tasks