Overview
Research
in my lab investigates the neural basis of animal behavior:
We are interested in
identifying and examining
neural circuitry that underlies offensive
and defensive aggression as
well as decision-making
and behavioral choice.
We use crayfish as our
primary
animal model because they display easily quantifiable behavioral
patterns, and
they feature a nervous system of tractable complexity that is
accessible for
a variety of neurophysiological and neuropharmacological studies.
Most
social animals compete aggressively for resources such as food, shelter
and mates. The early stages of an encounter between well-matched
crayfish are marked by an aggressive escalation that can include
strikes, aggressive posture, grappling with claws, and bouts of
offensive tail-flips (Herberholz et al. 2001, Edwards & Herberholz 2005). At
some point, fighting in crayfish is interrupted by an abrupt change in
the agonistic behavior of one animal as it switches from aggressive to
submissive behaviors. This switch marks the change in the dominance
status of the animals and identifies the new subordinates (Herberholz
et al. 2001). Dominant and subordinate crayfish then show
clear differences in their behavior. The dominant animal displays a
dominant posture, initiates approaches and attacks, constructs a
shelter and claims first access to most resources, while the
subordinate displays a submissive posture, retreats and escapes from
the dominant, and is left to claim unwanted resources (Herberholz et
al. 2001, Edwards et al. 2003, Herberholz et al. 2003, Song
et al. 2006, Herberholz et al. 2007).
Recently,
we found that the stability of dominance relationships is
context-dependent. A small change in the social environment, i.e. the
presence of another crayfish, quickly disrupts dominance relationships
and facilitates reversals of social status (Graham & Herberholz 2009).
In our
attempt to understand the behavioral
mechanisms underlying social dominance, we use video analysis to
identify aggressive
and submissive behaviors that are expressed during agonistic
interactions in
pairs and groups of crayfish. We combine this with non-invasive
electrophysiology,
intracellular electrophysiology and neuropharmacology to investigate
the neural
circuitry responsible for dominant and subordinate status.
When attacked by a natural predator (e.g., dragonfly
nymphs), juvenile crayfish produce three different forms
of escape tail-flips controlled
by as many neural circuits (Herberholz et al. 2004a).
Two
of the tail-flips are mediated by
giant neurons (medial giant and lateral giant) that evoke stereotyped,
reflexive escape responses away from the
stimulus. One is mediated by non-giant circuitry that
produces tail-flips of less stereotyped forms with longer response
latencies. The neural circuits that control the tail-flip behavior are
only partially understood (Herberholz et al. 2002, Antonsen et al. 2005, Herberholz
2009). We are
interested in how the different escape circuits integrate sensory
signals and how they interact with each
other to produce effective behavioral outputs (Liu & Herberholz 2010).
We are also interested in decisions-making
processes that take place in the nervous system and lead
to adaptive behavioral
choices. By combining video- and electrophysiological recordings, we
can measure behavioral
and neural responses to simulated predatory attacks. We
expose juvenile crayfish to moving shadows while
the animals are searching for food. In response to approaching
shadows, each crayfish produces one of two discrete behavioral
outputs: it either tail-flips backwards by rapid flexion of its
abdomen or it
immediately stops forward locomotion and freezes in place (Liden & Herberholz
2008).
By using a non-invasive
technique to record neural activity (Herberholz et al. 2001, Herberholz et al. 2004a, Herberholz
2009)
we are able to identify the underlying
neural circuitry that controls the tail-flips produced in response to
shadows. When exposed to different predator (shadow) signals
combined with food incentives of different qualities, crayfish make
suprisingly complex decisions by carefully balancing risk against
potential gain; this identifies crayfish as a new and important model
to study value-based decision making (Liden et al. 2010). The
different components of the circuitry are accessible for intracellular
electrophysiology, and we are planning to test the effects of
neuromodulators on these circuits. In addition, we are currently
investigating how internal states of the animals (e.g., social,
motivational, and developmental)
affect the decisions that lead to discrete behavioral choices.
To identify discrete patterns of
neural activity that are correlated with status-related
behaviors and decision-making, we use manganese-enhanced
Magnetic Resonance Imaging (MEMRI).
Manganese,
a paramagnetic contrast agent and calcium
analog, can highlight active
brain areas.
Preliminary
experiments with live crayfish
have shown that they are well suited for MEMRI
studies because they have no
blood-brain barrier and can easily be restrained
within the imaging apparatus. Crayfish
tolerate long imaging sessions in high magnetic fields, and they can be
placed in
small imaging coils which results in images of
very high spatial resolution. We
have previously demonstrated the feasibility
of MEMRI for
identification
and reconstruction of neural structures in crayfish; thus,
manganese can
be used as a contrast agent for crayfish neural tissue (Herberholz
et al. 2004b).
Recently we found that MEMRI can also be used to
visualize functional uptake of manganese into brain areas of live
juvenile crayfish. Stimulation of one of the animals' antennae led to
localized unilateral labeling in areas of the brain that received input
from the stimulated antenna. This shows that MEMRI has the potential to
allow identification of stimulus-evoked neural activity in live animals
at near single-cell resolution (Herberholz et al. 2011).
Projects
Current projects investigate :
1.
Mechanisms underlying decision-making and behavioral choice
2. Mechanisms underlying formation and maintenance of
dominance relationships
3.
Neural circuit organization
& multi-sensory integration
Welcome to the
Laboratory of